Disclaimer : No, I don't own Doctor Who, Jack, or anything like that. Wouldn't it be cool if I did, though?

A/N : Wow, this is…way fluffier than I usually write. It includes slash, it includes the Jack/The Doctor pairing; if you don't like that kind of thing, spin on your heel and leave. I can't be bothered dealing with slash-flamers this time around. Don't like the pairing, don't read it.

However, any constructive criticism, on my characterisation, writing style, or anything like that, is always appreciated.

On with the story.

"I'm leaving."

Those two words meant so much. They changed the future, changed the universe, sent everybody's lives spinning off on an unknown course.

The Doctor couldn't fit that idea inside his head. Jack was leaving. Jack, who was standing in front of him by the TARDIS controls looking so perfectly alive and here, was leaving. Running. Abandoning both him and Rose.

The two words hit him hard, and he heard the muffled squeak that came from Rose by his side. Jack. Leaving. Jack. Gone. It just didn't seem right; the Doctor had known that he'd leave eventually – everyone did, no one could stay around forever – but he hadn't expected it to be so soon.

Some part of him thought that he should have known. That he should have seen it, predicted it, somehow. But he hadn't. He'd thought that Jack was a keeper. He really, really had. He had…something. That same something, that spark, that Rose had. The Doctor had never been able to pin down what it was that he looked for in his travelling companions, but both Rose and Jack had had it.

Except, now Jack was leaving. Of his own accord. It wasn't like Adam, it wasn't like he was chucking Jack out. That would have been alright. That would have put the Doctor in charge, and that was fine. But this wasn't something he was in charge of, this was out of control and he wasn't sure how to react to it.

He kept his eyes trained on Jack's face, even when Jack squirmed under his heavy gaze and even when he felt Rose glancing towards him. No expression on his face, just rolling this over and over in his mind. How to react, how to react? What did he say? Do? Did he beg Jack to stay? He wanted to, boy how he wanted to, but it didn't seem very…dignified. If Jack wanted to go, he was free to.

All the same, the Doctor couldn't help but wonder why he'd thought it was a good idea to take Jack and Rose to Monalie in the first place. He'd seen the vague flicker – it had only lasted for a second, but it had been there – of memory on Jack's face, but he hadn't registered it. Hadn't registered it until it was far too late and some strange American was already talking in his obnoxious voice, already making offers Jack couldn't refuse, already stealing Jack away from them.

"Jack Harkness? Captain Jack Harkness?" They'd been staring out over a cliff, each lost in their own thoughts, when the voice rang out from behind them. An accent identical to Jack's, and out of the corner of his eye the Doctor could recognise the expression of intense surprise on Jack's face.

It was wiped over quickly, and by the time the three of them had turned around to see a blonde haired man wearing an ecstatic expression, Jack's old smile was in place. Where other people went blank when they were worried or scared, Jack just grinned. "One and the same." Jack answered.

"Holy shit!" The blonde had exclaimed, and then there'd been the hug. More like the grope. Clinging tightly, with that stupid blonde's hands roaming to places he had no right to even look at. The Doctor had felt a familiar stab of jealousy, an emotion usually reserved for the various 'boyfriends' that Rose occasionally paraded around in front of them.

"You two, y'know, know each other then?" Rose asked, which gave Jack the opportunity to disentangle from that hug-grope.

The stupid blonde allowed his eyes to rake over Jack's form in a way that made the Doctor seriously consider giving him a black eye. "Intimately," Stupid-blonde purred. Jack looked down at the ground, shifting on his feet. "Thomas Cunningham," he introduced himself, eyes leaving Jack momentarily to scan over the other two. The Doctor picked up on the barely disguised sneer, which only added to his reasons to hate this man.

"Right. Go ahead andpack your stuff then. Wouldn't want to keep Thomas waiting, would we?" His voice didn't quake or shake or break or doing any of the stupid things he'd expected it to. He wished that it had. Then maybe Jack would have been convinced that he had to stay, that the Doctor wasn't even sure if the TARDIS would want to run anymore with him around, that the Doctor wasn't sure if he would want to run anymore either.

He turned away then, fiddling uselessly with one of the many buttons on the control panel just so that he wouldn't have to look at Jack any longer. He couldn't look at the face he'd learnt so well, or at the eyes that always and now would always hide everything. He'd once planned on coaxing Jack's secrets out of him, one day. Guess that day just wasn't going to come.

"Okay. 'though, just for the record, this doesn't have anything to do with him." The Doctor could hear the thread of anger in Jack's voice, but before he could reply the sound of footsteps followed the words. Jack was really doing it then. Really packing up and jetting out.

The Doctor's absent movements on the control panel faded, and he just clutched at the side for support. Breath in through the nose, out through the mouth. You can't panic if you just concentrate on breathing. In. Out.

Three hours after meeting Thomas, and the Doctor had already decided that he really, really didn't like him. He didn't like the way he talked, the way he talked to Rose as if she was unimportant, and he hated the way Thomas looked at Jack. It was strange for him to feel this protective over him. Usually he just trusted that Jack could handle himself and left him to it. Rose took up all the worrying the Doctor had time for.

But the way Thomas looked hungrily at Jack, listened too intently during some of Jack's stories, and allowed any casual touches to become not-so casual just put the Doctor on edge. Something wasn't right. Something wasn't right at all.

He'd tried to ask a few subtle questions – why was Thomas here, what he was doing, why the hell his hand kept 'casually'brushing against Jack's – only to be fobbed off with vague and brisk answers. His uneasiness only grew when Thomas asked Jack if they could 'talk in private'. Talk in private? What?

Still, Jack had just nodded, "You two can keep yourself entertained for a few minutes, right?" He asked them, and Rose nodded enthusiastically. The Doctor didn't move, studying Thomas's face instead. The blonde sneered again, before placing a hand on Jack's elbow and guiding him away.

"Doctor?" Rose edged towards him. She sounded lost, confused. As if her tightly knitted future and plans were falling apart, just as the Doctor's were. Jack was leaving. That thought kept popping up at random intervals. Leaving. Deserting. Running. Gone. "Doctor, what…he's not really going. He can't be going."

"Yes, he can. He is."

"But…he's not. You can stop him, right?"

"Stop him how, exactly? Barricade him inside his room?" Hey, now that was an idea. As long as the Doctor was in there with him, alongside a big bed and a bottle of wine. Actually, forget the wine. The bed sounded too tempting. "Doubt he'd thank us for that, Rose."

"But…you're the Doctor. You'll fix it. Fixing things is what you do."

"Fixing things, Rose. I don't think Jack'd like being referred to as a thing." Nor did the Doctor think that this was something he could just 'fix'. He couldn't just wave his sonic screwdriver at Jack and have him come to his senses. Although, right now, he was ready to consider just about anything.

"Yeah, I know. But you have to do something. You're not just going to let him walk out. With Thomas?" Rose took a few steps forwards, but the Doctor didn't turn around. His eyes stayed focused on the panel, his hands tightened against the side until his knuckles went white. He didn't want to think about this. He just wanted Jack to hurry up and leave so that he could get on with…with everything. "Doctor?"

"Rose, there's nothing I can do."

"Yeah, but…Can't you, like, talk to him or something?" Talk? Talk? She was the human, shouldn't she be the one that had to talk? The Doctor wouldn't know what to say, what to do.

Despite this, he shrugged and turned around with a wide grin on his face. "If you want me to." She nodded, and the Doctor found himself tracing Jack's footsteps while trying to think of what he was supposed to say to change Jack's decision.

He'd strained to try and hear the conversation, but it was inaudible. Muffled voices, the occasional word was all he could pick up. You'd think that, if he was going to be stuck with ears the size of his, that you would at least get enhanced hearing to go with them. Unfortunately not, so the Doctor couldn't make out what they were talking about.

"So…where are we going next then, Doctor?" Rose asked from her seat beside him. The four of them had relocated to a small café – according to Thomas the food was amazing, but the Doctor hadn't touched anything yet – half an hour ago. Rose was nervous too, the Doctor thought, as she was fiddling and shifting in her seat even more than usual.

Thomas had taken Jack right out of the café to the opposite side of the road. It was difficult to even guess what they were talking about from their body language, but Jack looked angry. Real angry, which seemed odd. The Doctor's experience had proved that Jack was fairly easy-going. If Thomas had managed to stir that anger, he must have done something fairly bad. All the more reason to hate him.

A short walk down one of the TARDIS's corridors, and he was leaning against the doorframe of Jack's room. Jack didn't make any indication that he was even aware of the Doctor's presence; he sat on the edge of his bed, head in his hands. If the Doctor didn't know any better, he'd say the guy was crying. Oh, god. He hoped Jack wasn't crying – that would really put him out of his depth.

But Jack looked up, his smile on his face and those blue eyes notably tearless. Whew, that was good. No tears. The Doctor didn't speak, his arms crossed in front of his chest, as he considered what was supposed to happen now. He supposed Jack would dictate that.

"Don't worry, Doc, I'm almost ready to leave. I'll be out of your hair - " Jack's eyes slid up to the top of the Doctor's skull, in a way that made him desperate to check in the mirror for bald patches. " – in a couple of minutes."

"What if I don't want you out of my hair?" He took a step further into the room and closed the door behind him. "What if I think you should stay in my hair?"

He'd never seen a more sceptical look on Jack's face. "Don't." The Doctor watched in confusion as Jack shook his head, stood up, and paced around to the other side of the bed. "I know you don't like me, Doc. And don't bother denying it. I'm only here 'cause Rose likes me."

The Doctor snorted at that, "I like you too. And Rose doesn't dictate who stays on the TARDIS. Otherwise, we'd have Jackie and Ricky following us constantly." Urgh, and wouldn't that be fun? Then he'd end up being the one leaving. "As we don't, you can stand assured that I want you onboard."

Jack shook his head, but didn't talk. Stayed silent. The Doctor didn't like that at all; Jack wasn't the 'strong, silent' type. And thank heavens. He'd gotten quite used to the constant banter that spilled from Jack's lips. This loaded silence was just unnerving. It clenched his stomach, sped his hearts up in a way that even staring straight at a dalek didn't. The silence reminded him of how much of a mystery Jack was, and how much of a mystery he'd always be, unless the Doctor somehow convinced him to stay.

"Come on, what can Thomas offer you that Rose and I can't?"

Jack wasn't quite yelling, but there was definitely anger in his words. Probably closer to a hiss than a yell, the Doctor mused from where he sat, still observing the pair through the window. Thomas was still wearing that ridiculous smirk, obviously amused with whatever it was that Jack was ranting about. Smarmy bastard.

"Doctor?" Rose repeated, as Thomas reached out his hand to clamp it tightly around Jack's wrist when Jack tried to walk away. The Doctor straightened up, and was halfway out of his chair when Rose's hand on his shoulder pushed him back down. "You're kinda creeping me out, okay? He's gonna be fine without you there to stand up for him."

She was right, of course. Despite her lack of even the most basic knowledge of time travel, Rose was smart. With the Doctor watching, Jack jerked his arm out of Thomas's grip, spitting out one more angry comment.

Thomas's smile didn't alter or fade. Instead he took a calm step backwards, his mouth moving casually. The Doctor squinted, still focused on the scene unfolding in front of him despite Rose's protests. Jack had stopped talking, as apparently it was Thomas's turn. Bloody Thomas.

A few more minutes of discussion – during which Thomas pointed back at the café at least twice, which was curious – Jack shook his head and began to walk away, to return to the café, and Rose, and the Doctor. Thomas didn't follow, instead he turned to walk down the street and away. The Doctor couldn't help but feel a buzz of warm satisfaction.

Jack didn't answer, he just shook his head instead. The Doctor wasn't sure whether to smile indulgently or slap him upside the head. Human could be so…complicated sometimes. So complicated and so simple. You'd think that, after 900 years, he'd have finally made some progress towards figuring them out. However, that didn't appear to be the case. As he leant against the wall, watching Jack intently, he couldn't figure out what on earth was going on in that head.

Which bugged the hell out of him, obviously. The Doctor didn't like unsolved mysteries. He liked solving them, but he didn't like the ones he couldn't solve. And Jack? Or humans in general? He doubted he'd ever be able to figure them out.

What he had figured out was that, given enough space, humans talked. A lot. If you stayed quiet for long enough, they'd fill up the time with inane conversation. Weather. Sports. TV. Small talk. Chit-chat.

"Doc, I don't know what you want me to say." Jack said, after a long pause. Okay, that wasn't quite as meaningful and soul-searching a confession as the Doctor had hoped for, but it was a start.

He shrugged, and pushed himself away from the wall to take a seat on the bed next to Jack. "Say you'll stay." He asked. He looked down at his hands as he talked, mimicking Jack's own posture.

A weighty sigh, a slight chuckle, sounded from beside him. He felt rather than saw Jack shaking his head, and internally frowned. He couldn't just give up, Rose'd kill him for a start.

But that wasn't the whole reason. Jack fit with the TARDIS, and with Rose, and with him. They just all blended together well. Perfectly. Jack just worked, clicked. Although the Doctor, Rose and the TARDIS would be able to trundle along without him, it'd feel like there was a gaping hole. A jigsaw missing a piece.

But it was more than that. It had to be. Only something more than that would explain the lump that surfaced in his throat every time he thought of this bed being empty at night.

"Look, I know you said that you don't mind me being here," Ah! The silence ploy had worked. Jack was talking. The Doctor was getting somewhere. The world was good. At the moment, anyway. "But that's kind of the point. You don't mind. You're indifferent. If - "

The Doctor kissed Jack before he had time to tell himself not to. He swept in, striking as fast as a snake, and their lips brushed. Not hard, barely a kiss. Hot breath mingled, and Jack stopped mid-sentence. The Doctor moved his head back an inch or two, and waited. Waited to see Jack's reaction, waited to see if this changed things the way he wanted it to.

"How's that for indifferent?" The Doctor eventually asked, when it became apparent that Jack wasn't going to speak unless prompted. His head still hovered just a few inches from Jack's, lips touching as they talked. He couldn't wipe the wide, and probably insane, grin off of his face.

Asmile – genuine, not the forced ones that Jack seemed to have been sporting recently – popped up in front of him. His mind screamed in triumph; somehow, he just knew that with that one kiss he'd changed the future. Maybe not the actual future, because that would have been bad, but his future. Their future. "Maybe you're not as quite uninterested as I thought."

Their mouths crushed together again, and this time it was stronger. More forceful. More desperate. Hands sneaked under clothes, over skin, through hair. Jack's mouth opened a precious few inches, and their tongues clashed. Time seemed to speed up and stretch out, warping mindlessly out of control. His pulse raced, growing ever stronger as Jack moaned into his mouth.

Stop it, you're using him. He's supposed to be a friend, a companion. Nothing more, nothing more, never anything more. It's the rule. Look, don't touch. Want, don't have.

Protests were still whirling around in his mind when Jack lay down andpulled the Doctor on top of him was he did so.The Doctorpulled backwards, breathing desperately as he looked down at Jack's confused expression. Flushed lips, mussed hair, sharp angles of his face. It took a lot of self-restrain not to just brush all reservations and doubts from his mind and carry on without a care.

Jack's hips bucked up, grinding their groins together. A startled moan escaped the Doctor, and that was the precise moment that he knew he wasn't walking away from this. He could tell himself hundreds of reasons not to, why the best course of action would be to stand up, walk out, and allow Jack to leave without trying to stop him. He knew all of those reasons. But he didn't care.

His grin reappeared on his face, straining at his cheeks. Right, he reckoned he could hold back for another few minutes, and then the dam was really going to break and drown them both. "So you're going to stay?" He asked. One hand was spread flat on the white bed sheets, while the other was lying passively on Jack's flat stomach, buried underneath the black t-shirt he wore.

Jack chuckled breathlessly. "Hell, yeah,"

"Great. In that case, we have a few new rules to go over," The Doctor was surprised to find that his voice sounded completely normal. Cheery, quirky, with that Northern accent shining through strongly. The turmoil of emotions that swirled around inside him was carefully hidden behind his grin, behind his speech, behind his mask.

Jack's face darkened with mistrust, and the Doctor knew he was going to have to be careful here. One wrong word, one wrong move, and Jack was gone. Skipping off to live happily ever after with Thomas. And he did not want that at all, so he was going to be very careful.

"First rule : if you threaten to run off again, I get to tie you up until you come to your senses," Ah-hah, a half-smile quirked at thecorners of Jack's mouth. "Actually, second rule : I get to tie you up sometime anyway." Wider smile. That was good. The Doctor paused momentarily, just watching and revelling in the butterflies dancing in his stomach. Butterflies. Surely he was too old to be acting like a love-sick teenager.

"That it?" Jack startled him out of his thoughts.

"Not even close. Are you always this impatient?"

"Pretty much."

The Doctor nodded at that answer; well, that was to be expected. Humans didn't like to wait long for anything – their life spans were too short. Shame, really. Nothing more than a flash in the timeline.

Jack raised a quizzical eyebrow, and the Doctor jolted himself to get on with these new rules. "Rule three : you're through in my bed from now on. This room's way too small," It wasn't, not really. And if it was, the TARDIS could have altered it in a blink of an eye to a more suitable size. But, who cared about the technicalities? Jack was sleeping in his bed from now on, no argument about that. "And…rule four : you have to tell Rose that I'm a hundred times more 'Spock' than you are."

"What?"

"You heard me."

"No way."

"Then I'll just chuck you off the ship."

"Liar."

"Yup." The Doctor cut off any argument by kissing Jack again, moans and hurried breath sounding from both of them. He grinned at the solid feel of the body underneath him, finally content in the knowledge that Jack was not going anywhere for a long while yet.