Disclaimer: I don't own Supernatural.
A Moment of Enlightenment
Dean didn't know what to expect. He waited patiently for Cas to stumble in through the door, trench coat undoubtedly smeared with dirt and blood, and his face, etched with hunger and worry, lighting up at the sign of Dean's waiting form, but the bleak years of hunting monsters and waiting Dad or Sam had taught him one valuable lesson: expect nothing. As the days began to roll on without sight or sound from Cas, the pessimism only built up until he stopped waiting, started spending his time searching for cases, chastising Crowley or pestering Kevin about his progress, and the possibility of Cas actually returning became smaller and smaller.
When Cas eventually turned up, not sporting the characteristic trench coat that Dean expected, he only felt a greater sense of loss. Cas had returned, but it didn't seem, or feel, like Cas had, only some human shell that spoke in the same monotonous, gravelly tone, and used the same, often archaic expressions. There were so many questions running through his mind, about what to say and how to offer comfort and how to greet that he forgot to do anything, just stood there, gaping, while Sam pulled Cas into a bear hug.
"Cas, man, it's good to see you," he said, patting the angel - man - in question on the back, "you'll be safe here."
Cas didn't seem even remotely comforted, just more conflicted. His dirt-covered brow drew together in thought, and his eyes drifted from Dean's face to stare vaguely ahead.
"I'm responsible," he pointed out, and Dean would be lying if a small part didn't agree. Cas could have fixed Sam, wouldn't have caused the constant threat of infuriated angelic attacks that they'd no doubt come across.
And Sam was staring at them with a strange expression. Dean really had no idea what to do or what to say. Claim it didn't matter? He'd be lying. It wasn't his fault? Another lie. They didn't even know if they could fix it, and it was pretty obvious that Cas could tell.
"I'll get you something to eat," Dean muttered and trailed out like a kicked dog, feeling more shame than he had in a long time, wanting to just disappear back into his room and clean his guns like their biggest concern had been the trials. He could hear Sam striking up a conversation with Cas behind him – asking about what had happened – but Dean blocked them out, focusing instead on pulling out the most recent leftovers and a bottle of water.
When he returned, Cas was sitting at the table looking ready to pass out, and Sam was staring at him in concern and Cas, in return, watching Sam, like some unrelated tragedy had brought them together. Sam stared at Dean as he entered, gave a slight grimace, got up and left the room, saying he should probably make sure Kevin wasn't trying to exorcise Crowley again. Dean took a seat on the opposite side of the table, letting his arm cross and rest in front of him.
Cas wolfed it down faster than he thought was possible or healthy, completely ignoring Dean's "at least take the time to taste the food". Dean fidgeted with his hands, trying to ignore the feeling that he owed Cas something. Eventually, the words vague but ultimate meaning clear, he said:
"Look man, I don't know what you did, but we can work through it. You're with us, and I don't care if I have to go through every damn angel on the planet to make sure it stays that way."
Cas stopped moving, his hand lightly brushing against the edge of the table, as though he were about to eat but was frozen in the moment.
"They're lost, Dean. It's my fault, and it should be my duty to help them."
"We can do that," Dean promised, "but first we have to make sure you're okay, and the junk-previously-in-my-trunk doesn't become a bigger problem than he's worth."
Cas still wasn't eating, only staring at the food, conflict written across his face. He made several attempts to speak, but each time he refrained, and Dean whatever it was, it'd be the last thing he wanted to hear.
"Uriel told me to stay in heaven. But I felt responsible for you, like any failure of yours was a failure of mine. Pulling a human out of hell, I never realized the impact it would have, on how I-"
"- I know," Dean said, and Cas' mouth pressed shut. He stared back down at the food.
"I'm tired, Dean," Cas eventually murmured. Dean nodded and gestured for him to stand, and led him from the main room off to the side of the building where the bedrooms were located. He pointed out his own, in case Cas needed anything, but Cas didn't seem to pay much attention, only swayed from side to side as he walked, hardly conscious. When Dean led him in to the room, he collapsed on the bed and subsequently didn't move, and Dean felt like an intruder on something so oddly personal. As a last thought, he removed Cas' shoes and returned to his own room, sitting in the dark and staring blankly ahead. The dynamics in his relationship with Cas were shifting, had been in the limited amount of time between Cas' arrival and his passing out on the bed, and Dean wasn't quite sure what to expect.
He eventually fell into a troubled sleep, still reclining against the headboard and still feeling that impending sense of change.
When it happened, Dean had expected it, but had still been surprised. He'd tried to avoid Cas for the entirety of the week, spending his time locked in his room and cleaning guns, or out on runs for food or standard salt and burns. Cas had tried to get him to speak, followed him around like a lost puppy for the first day begging for instructions, but he'd since then faded away into the background, become so scarce that not even Sam knew where he was. And Sam didn't comment. Not to Dean, at least.
When Cas appeared above him, pupils blown and expression twisted into something entirely human and entirely familiar, Dean was left in a state of complete shock. He was reclining against the head of the bed, dozing off when Cas entered, determination evident, and flung himself across Dean's body, gently his forehead as though Dean was some precious, breakable doll. He had the inquisitive look on his face, seemed to twitch with energy but looked as though a single shake of the head from Dean would send him away indefinitely.
Dean stared at Cas, felt the weight on his chest quell his turbulent fears of change, how the position seemed more comforting than out of place, and nodded once.
Cas was pouncing in a second, his lips attaching to Dean's skin and gripping his shoulders hard enough to cause pain. Dean grunted, hands going to Cas' chin to push his head up, and drive their mouths together. The rub of Cas' stubble against his face made his face twitch from the sensation, and dark hair felt strange to run his fingers through when it ended so suddenly. Cas' lips were bitten and rough, and he wasn't the experienced kisser that Dean was used to, but he picked things up quickly, didn't complain when Dean pulled away and maneuvered him onto his stomach, and didn't back out when Dean slipped the first cold, lubricated finger in. When Dean took him, he was turned over and spread out on his back, a dazed look on his face and whimpers erupting incessantly mixed with moans and gasps. He latched on to Dean's back the entire time, face looking delightfully contorted in pleasure and legs hoisted up, wrapped around Dean's body in desperation, chanting a chorus of "Dean", "more" and "please" like Dean had never heard before.
When Dean came, he reached down and brought Cas to completion, watching the muscles spasm in what Dean assumed to be the first experience of sexual pleasure in his life. Cas didn't pull away after, despite being sticky, covered in bodily fluids and a bed that was too small for the both of them, but relaxed against Dean's arm, stroking mystery patterns into the skin as Dean slipped into sleep.
Kevin watched them enter the room from the table the next morning, a wicked smirk adorning his fatigued face. Sam was busying himself with the paper, but his lack of squinting made Dean think his attention was also cast on them, and Dean had a sinking feeling in his stomach.
"So," Kevin said, exchanging a comical look with Sam, "how'd it feel to sink in to the feathery angelic passion?"