Sirius began joining them regularly for meals. It had become such a normal thing that Decima stopped congratulating herself for not doing something stupid after every meal. One night after dinner, however, an owl was waiting on her bed with a note.

Decima,

You owe me two meals. Breakfast and lunch tomorrow?

-S

Her heart stopped. She had almost forgotten her end of the bargain. She scribbled back that she thought that would be fine and mentally prepared herself for the impending social doom of sitting at the Gryffindor table, with the Marauders, no less. When she woke in the morning, she felt far from rested and all she wanted was to crawl back under the covers, for more reasons than one.

Decima made herself up carefully, slipped the still-sleeping Gwen an explanatory and apologetic note, and made her way up to the entrance hall taking deep, calming breaths. When she reached the entrance to the Great Hall she froze, staring at it. Maybe there was still time to run downstairs again and say she overslept. Maybe she could end the whole arrangement. Her stress levels were high enough from O.W.L.s and Sirius wasn't helping.

Just when she was about to turn and run, she felt hands hold her wrist from behind and a voice in her ear said, "Are you going to just stand here, or will you allow me to lead you to the food, love? I swear the toast is more attractive than the doorway."

Decima just rolled her eyes and pulled herself free from Sirius's gentle hold, marching into the Great Hall and turning to face him.

"Well?" she huffed. "Aren't you going to show me where to sit?"

He chuckled and said, "My pleasure, love." He led her to a seat across from Lupin and motioned for her to sit.

Potter, who was next to Lupin, said, "Wow, I thought you were joking, Padfoot. I didn't think you were actually going to bring Zimmerman to breakfast."

"What did you think I meant, Prongs?" said Sirius dryly as he poured Decima some juice.

Potter just shrugged.

"You look lovely this morning, Decima," said Lupin politely over his toast.

"Thank you, Lupin."

"Call me Remus, please."

She just nodded. The Marauders were putting her on a first name basis. Sirius must have noticed her shifting uncomfortably because he put a hand on her thigh and began telling jokes, which the other boys quickly joined in on. Soon, Decima was laughing and enjoying herself like she did this every day.

In fact, things went very well until Regulus arrived. He stood at the entrance of the Great Hall and dropped his bag with a loud thud when his eyes hit the Gryffindor table.

"Ugh," Decima said, careful not to look at her boyfriend. "He's going to kill me."

Sirius's face darkened.

"He'd better not touch you."

"Please, just ignore him," she muttered. "I'll be fine. I'll calm him down later."

James buttered himself another piece of toast and said, "So you didn't tell him you were eating with us?"

"Uh, no," Decima said. "That would have been a lovely conversation. 'Hi, babe, I'm going to start eating with the Marauders on a semi-regular basis at the request of your brother. See you in class.'"

They boys laughed and Sirius leaned in and whispered softly, "Just like you haven't told him you've been dreaming about me, love?"

She blushed furiously and busied herself with eggs, but he just smirked and winked at her, making her blush even more furiously. So now he knew she was dreaming about him. Maybe she'd have to fabricate her own knife story.

"Well," she said, "I'd best be getting to Potions. I've already been late twice and I'd like to pass my O.W.L.s. Besides, I need to mentally prepare for a cranky Potions partner. See you at lunch!"

"I'm looking forward to it," said Sirius, who smiled softly at her. She could feel his eyes on her until she turned the corner after leaving the Great Hall.

Regulus was already in the dungeon, scowling down at a random page of his Potions book. Decima sighed and slid into the seat next to him, laying a hand on his shoulder.

"Hey, baby," she said.

He looked up with a glare.

"What the hell were you thinking, CiCi? What's going on with you?"

She sighed. She had to think fast and get approval from Sirius later.

"It's nothing, sweetheart; your brother is just helping me with Transfiguration. I'm having lunch with them, too, but I won't do it all the time. It's just occasional."

Regulus was still frowning, but he couldn't seem to find fault with her story. He shook his head and kissed her on the forehead.

"You could have told me, love. You scared me; I thought he was taking you from me."

Decima scoffed.

"As if that would ever happen."

At lunch, Decima slipped into the seat next to Sirius again, who grinned at her as she sat.

"How was Potions?"

She shrugged.

"He's not mad. But you'll be pleased."

His smile faded a little and he looked slightly suspicious.

"Why?"

"You're my new Transfiguration tutor, congratulations."

They all laughed and Sirius said, "Well, love, I suppose that means we'll be seeing a bit more of each other."

She sighed.

"Don't hold your breath, Sirius. This doesn't mean anything."

He grabbed a second sandwich and said, "Really? Lying to your boyfriend, ditching your friends, sitting with the Gryffindors, and having sex dreams about me all means nothing?"

Remus choked and sprayed sticky pumpkin juice.

"WHAT?"

"I never said anything about sex dreams," said Decima, though rather less insistent than she ought to have been.

Sirius smirked.

"So you just turned red for nothing? Why don't you just admit that you want me?"

The other three Marauders were watching in shock.

"Because," she said, "I don't."

But her voice was weak and noncommittal. His smirk only deepened.

"You don't sound very sure of that, love."

She wasn't. In fact, she was almost positive that she did want Sirius, but she was nowhere near ready to admit it. He leaned in and whispered in her ear, softly, "Tutoring starts tonight."

Decima was about to ask what he meant, but Remus noted that it was time to go to class and she didn't get the chance.

She sat with the Slytherins at dinner, but Sirius didn't join them and she didn't really enjoy herself. Regulus seemed to be making up for lost time and had his hands all over her, but she wasn't in the mood. Several minutes in, Sirius came over, but he didn't sit down.

"Hey, Decima, study session after dinner? I found that book I wanted to show you."

What game was he playing? Regulus didn't appear suspicious, so she nodded.

"Great," said Sirius, with his best smile. "Meet me in the library."

Christa snorted.

"This is way too weird, for me, Black. I mean, I know you're great at Transfiguration, and all, but since when do you tutor, and have you ever even set foot in the library?"

Sirius leaned down and winked at her.

"Ah, Rosier, that just shows how little you know about me."

And with that, he returned to the Gryffindor table, but Decima could feel him watching her the entire meal with hungry eyes. At one point, she caught his gaze and he smirked at her, licking his spoon thoughtfully. She nearly shuddered at the heat in his gaze.

Maybe she shouldn't have agreed to meet him, after all.

Nevertheless, after dinner, she trudged up to the library and found a seat, flipping through a book, but not really paying attention to it. Her heart was absolutely pounding.

After several minutes, Sirius marched up to her, grabbed the book out of her hand, and set it down on the table. The look he gave her was the same he had given her in Regulus's bed. Before she had a chance to say a word, he brushed back the hair from her face and caught her lips in a forceful, passionate kiss.

Somehow, they were both standing, though she didn't recall leaving her chair, and he pushed her up against the bookshelf exploring her mouth with his tongue. She should have pushed him away. She should have smacked him. Instead, she let him run his hands all over her, groping and squeezing feverishly. She let him work his hands under her shirt and across the tender flesh of her stomach. She trembled. His hand grazed the underside of her breast and she moaned into his mouth.

Sirius pressed his body harder against her and began to grind his hips. Decima gasped, feeling his need pressed hard against her. This needed to stop, but she didn't know how to make it stop, and she wasn't sure she wanted it to. Regulus had never touched her like this.

After a few more minutes of kissing, touching, and Sirius grinding into her, Decima realized that she was standing in the middle of the library, cheating on her boyfriend with his brother. She wasn't sure if she was gasping from this realization or from the delicious pressure his tongue was applying to her collarbone, but she knew it need to stop before she lost her head completely.

She pushed him back and he paused before moving toward her again. She pushed him again and he whimpered.

"C'mon, Decima, please."

"Sirius," she whispered, breathless, "we can't do this. We just can't. I should go."

She grabbed her bag, but he grabbed her arm.

"No, don't do this. We can come to some kind of arrangement." His eyes pleaded with her to stay, and she almost dropped her bag, but she reminded herself of this situation and shook her head, shaking her arm loose from his grasp and rushing out of the library. That look he had given her was heart-breaking.

Decima straightened her robes, flattened her hair, and hoped she didn't look as though she had just been snogging. The moment she got back to the common room, Regulus said, "How was studying?" without looking up, and Decima grabbed his book, tossed it aside, and sat on his lap, pressing her lips tightly to his. Only then did she realize she had just mimicked Sirius, but it didn't matter, because Regulus responded perfectly. He wrapped his arms around her waist and pulled her closer to him, licking her lip lightly.

She shuddered and parted her lips, allowing his tongue into her mouth. It was strange how alike those brothers were. Regulus's tongue explored her mouth in almost the same hungry path as Sirius's had not long ago. However, Regulus pulled back.

"You taste different."

Uh-oh.

With a sight, Decima took his hand and led him to his dormitory, which was thankfully empty.

"I need to tell you something, but you need to promise me not to overreact, all right?"

Regulus frowned and nodded and Decima pressed onward.

"Your brother has been trying to seduce me since start of term."

"WHAT?"

"Calm down, Regulus, he hasn't gotten me, and he won't," Decima sighed, not sure she believed her own words. "I like to talk to him, but he's not you. And I think I made that clear to him."

Regulus pulled her onto his bed.

"You're mine, Decima. I don't want him touching you." He rubbed the back of his neck, thoughtfully. "Maybe having you stay over Christmas is a bad idea."

"No," she said. "Don't let it bother you, sweetheart. Don't let him ruin our plans."

Without responding, Regulus pulled her into a feverish kiss, rougher and more urgent than usual. It was more like a kiss from Sirius. Decima gasped as he pushed her down, got on top of her, and undid his tie.

"Regulus, what are you doing?"

"Marking my territory," he growled as he practically ripped his own shirt off. He moved to under her buttons and she squirmed.

"Are you sure, sweetheart?"

"Don't try and talk me out of it, Decima. I want this, and I know you do, too."

She didn't argue. She didn't say anything at all as he went along, ripping the rest of their clothes off. He gazed hungrily down at her for a moment before placing hot kisses all over her body. She ran her nails down his back and she could feel him hardening against her leg.

"Oh, Merlin," she gasped as he teeth found their way to her nipple. She continued to moan and gasp as he rolled his tongue along her breast. Closing her eyes in bliss, she didn't even notice that he had shifted until his throbbing cock was being pushed inside of her. It hurt at fist and she cried in pain, but as he slowly worked in and out, the pain turned to pleasure and her cries took on a different meaning. It was almost as good as her dreams about Sirius had been.

Regulus quickened the pace and groaned as her hips bucked in time with his rhythm. He was so close, she could feel it, and as eh cried out, her entrance tightened around him, and they came together, panting heavily as his lips met hers sweetly.

As they curled up together in his bed, he pulled the covers over them and petted her face.

"You're mine, CiCi. I don't care if I have to curse every guy that looks at you; I don't want anyone but me touching this beautiful body ever again."

Decima nuzzled her face into his solid chest and sighed.

"I love you, Regulus."

"I love you, too, CiCi."

They cuddled and talked, and she fell asleep in his arms, peaceful and content, Sirius Black completely driven from her mind. That is, driven from her mind until morning.

At breakfast, Regulus ate with one arm draped protectively around Decima's shoulders, glaring at ever male body that passed, including his friends. She just calmly ate her eggs, hoping that she might have one day of peace, but she had no such luck.

In sauntered Sirius Black, looking better than ever, and Decima nearly dropped her fork. Regulus made an angry hissing noise as his brother sat in his usual spot, but calmed after a moment when Sirius began flirting not with Decima, but with Philomela.

Decima tried not to watch as Sirius made a show of whispering in Philomela's ear, nibbling on it gently as her eyes grew wide. Jealousy. That's what Decima was feeling and she couldn't explain why, because she and Regulus had been so happy the night before. Sirius saw met her eyes and smirked at her as he was leaving.

All day, a part of Decima wanted Sirius to surprise her in a corridor and kiss her again, but she had no such luck. After her confession, Regulus wouldn't let her out of his sight. He even walked her to the bathroom and waited outside the door for her, as though he though his brother might be lurking in the girl's toilet, waiting for Decima.

At first, it seemed sweet, but the protective behavior grew old fast. Regulus actually yelled at a sweet third year boy who asked if he could borrow her quill for a moment. She made Regulus apologize because the boy was crying.

When Regulus rejoined her on the couch of the Slytherin common room, Severus Snape, a greasy sixth year with a hooked nose, sat down next to Decima and a nerve was twitching in her boyfriend's jaw, but he didn't say a word.

"You got word about the time change?" Severus said. Regulus nodded and with that, Severus got up and left.

"What was that about?" Decima said, scribbling down the last of her Charms essay.

"Runes study group."

She frowned.

"Severus isn't taking Ancient Runes."

She detected a hint of nervousness in Regulus's blush.

"I meant Arithmancy."

"And why and I not a part of this study group?"

Arithmancy was easily her best subject.

"I – I…" he stammered. "Okay, look," he said finally, dropping his voice and glancing around, "there's no study group. I'll tell you when the time's right, but for now, you'll just have to trust me."

Not wanting to nod as though she was okay with this, she reminded herself that this time yesterday she was cheating on Regulus in the middle of the library. Reluctantly, she nodded. At least if Severus was involved, it was highly unlikely that he was using this time to see another girl.

"So," Regulus said, "what was that about at breakfast?"

She tensed.

"I don't know what you're talking about, sweetheart."

And then she leaned over and caught his lips in hers, but before she could deepen the kiss, Regulus pulled back.

"I'm not letting you off that easy," he said.

"What?"

"Oh, come on, Decima, any time you don't want to talk about something you try to distract me with a kiss. But I'm not doing it this time. You were jealous of her, weren't you?"

Did she really do that? She supposed she must, but not intentionally. Before she could lie to him about her jealousy, however, Gwen and Christa ushered Philomela into the common room and gave Decima a pointed look.

"Sorry, Regulus, I'm needed," she said, and followed the girls into her dormitory.

Philomela was in a state of shock.

"I thought he liked me," she said.

Decima sighed, sitting down next to her friend, really not wanting to know the details of her broken heart.

"FiFi, I need to tell you something about Sirius. He's been trying to shag me since term started."

"What?"

"He's trying to steal me from Regulus. I think it's some kind of twisted sibling rivalry. Anyway, at breakfast he was trying to make me jealous because I ran away from him in the library last night."

"It's not fair!" Philomela cried. "You've got both Black brothers tied around your little finger and the rest of us might as well not try!"

Decima frowned. What did that mean?

"What FiFi means," Christa clarified, "is that she feels inferior to your beauty and charm and is temporarily irrationally upset with you, but she'll feel better in a few days and we'll all pretend none of this ever happened."

Decima would have blinked in amazement, except this sort of thing happened yearly with Philomela, which was why Christa was able to give such a detailed translation. Gwen said Philomela had a complex. Decima though Philomela was complex.

Decima wandered back out to the common room to find that Regulus had disappeared. With a sigh, she gathered up her things and went to the library, hoping to be bothered for the rest of the night. Of course, she had no such luck.

She had no sooner sat down than Sirius Black had sat down next to her. Grumbling inwardly, Decima shielded her horrifically bad essay from his view as she worked.

"All alone in the library, Decima?" he cooed in her ear.

She shot him a glare.

"Bugger off, Black. You have no tact! Don't you know FiFi has a complex?"

He stared at her puzzled and she realized that what she had just said wouldn't make sense to anyone outside of her immediate circle of best friends. Decima sighed and dropped her quill.

"Look, Philomela has a yearly meltdown about her inferiority to me, and your treatment of her today triggered this year's. Congratulations. They usually don't happen until at least February. So she won't talk to me for the rest of the week and it's entirely your fault!"

Sirius just chuckled and shrugged.

"Ah, well, I'm sure she'll get over it. But I'm surprised my brother let you out of his sight. He's been quite protective today."

She blushed.

"Yes, well, he had a meeting. And he's got a right to be a little territorial."

Sirius's eyes darkened.

"What meeting?"

Decima shrugged absently, turning back to her essay.

"He won't tell me yet, but he said someday he will."

This didn't appease Sirius, who was still tense.

"You had sex, didn't you?"

Her eyes widened and she fixed them on her essay, determined not to look at Sirius.

"What–?"

"A brother knows," said Sirius with a shrug. "I'd still want that comparison shag."

She scoffed.

"Not a chance."

"Ah, well. So, what are you working on?"

She blushed deeply.

"Nothing."

"It doesn't look like nothing."

"Well, it is."

"It looks like an essay."

Before she could say anything he snatched the parchment from in front of her.

"Woah, what's this supposed to be on?"

She blushed even deeper.

"Animagi."

"You were right. You've got nothing."

Angrily, Decima snatched back her parchment.

"Well, I really am awful at Transfiguration. My needing a tutor was plausible. Anyway, I'm going to bed. Good night, Sirius."

And Decima gathered her things and left Sirius sitting in the library with a thoughtful expression that made Decima worry that he was about to do something to screw with her life again, and probably her hormones, too.