Dean knew the day Sam said yes because it was the first (and only) time Lucifer dropped into his dreams.

It'd been three years and Sam in his dream looked exactly as he had the day he'd left. They were sitting at a booth at an otherwise empty diner, and everything about it was so ordinary that it took Dean a moment to notice that Sam was staring at him with unusual intensity.

"Dude," he said, "What."

"Sam's image of you is taller," Sam mused. "You don't think very well of yourself, do you, Dean?" Which was weird, but as far as dreams went not so much, at least up until Sam leaned back and sighed and said, "I'm almost disappointed."

"Hold on," Dean started, because Sam was not allowed to talk to him that way, not even in his own subconscious, and then Sam said, "We both know you're not worth his loyalty," and something about the way he said it just-

-clicked.

Dean stood up sharply. "Lucifer," he snarled. Sam – Lucifer – waved a hand at him.

"Oh, sit down. There's no point in getting huffy. I'm just here to give you fair warning. As a favor to Sam, you understand."

Dean wanted his first reaction to be anger. His first reaction was actually despair, oh shit, Sam, what did you do what did you do. Lucifer watched him, expression almost perfectly one of Sam's, close enough to make his skin crawl. "Fair warning of what," Dean snapped, because it was the only thing he had, and Satan smiled at him.

"As you can see, Sam's come around. He said no for a long time – for you, of course – but I can be persuasive, and we understand each other." Lucifer looked momentarily thoughtful. Or maybe wistful. "It hasn't been a pleasant three years, though. I would have killed you for the suffering you put him through, Dean, but Sam is forgiving, and with Michael gone you are little more than an annoyance."

Dean bristled, despite himself, but overall it was overcome by an overwhelming feeling of heaviness. Sam had said yes. Sam had given in like Dean had always said he would, Sam had-

(Dean had been saying yes for months. Sam had lasted three years, alone.)

"It was his request," Lucifer was saying, "That I tell you. Convey his apologies. His love. He asked that from me, and one other thing – I promised him I wouldn't hurt you."

Dean stiffened. "You lied." Could he die, here? Could Lucifer reach out through his dreams and- but Lucifer – Sam – actually looked affronted.

"Of course not," he said. "I don't lie. It's a matter of principle. And I wouldn't do that to Sam. He's had enough of lies, don't you think?" A quick flash of Sam's smile, dimples and all, and it hurt like Dean desperately didn't want it to. "I won't hurt you, Dean. In fact, I have an offer for you." Dean gritted his teeth.

"Yeah? What's the offer?"

"You back down," Lucifer said, mildly. "End your resistance, and for Sam's sake I'll put you somewhere safe until this world is purged and remade. And at the end, I will let you see your brother again, and paradise." The single eyebrow Lucifer raised at him was both familiar and not in a way that made Dean's stomach turn.

"What do you get out of this?" Dean demanded. "If you're so sure I can't stop you-"

Lucifer looked at him with something like pity. "You truly think this offer is about you? My, Dean. You are a self-centered bastard. Just like Michael. No, if I leave you alive, it'll be for one reason, and that's Sam. I don't particularly like you, but Sam…I care more about Sam than anyone, and for whatever reason you matter a great deal to him. He doesn't want you to die, and honestly, Dean, I think by now he's suffered enough. Don't you?"

Dean felt sick. Lucifer smiled calmly at him. "You are irrelevant," he said, calmly. "Although, I must admit, Sam's request aside – I wanted to see what all the fuss was about. Sam talked about you an awful lot."

Dean's mind went blank. "When did you and Sam…talk?"

Lucifer shrugged Sam's shoulders. "Relatively frequently, actually. I was keeping an eye on him." Lucifer's stare was almost disapproving. "Since no one else was. He was lonely. We made conversation."

Dean didn't know why he asked. Didn't know why he didn't tell Lucifer to fuck off and get out of his head – maybe because looking at Sam's face, calm and relaxed and smiling, his brain was going in frantic circles of why why why did you let him go why why why and this was Sam's fault, this was Sam's-

"What did you talk about?"

Lucifer leaned his head back. "Oh, anything. Everything. College. Your father. My father. Michael. But mostly you." Lucifer's smile was…fond. "It was almost irritating at times."

Dean almost snorted. "Sam's like that." Lucifer looked thoughtful.

"He kept expecting you would make contact, you know," he said, idly. "Every time I visited, it was always maybe tomorrow. Maybe the next day. He never got tired of thinking of excuses for you." Lucifer shook his head, slightly. "Sometimes I thought I could like you, Dean. If it weren't for what you did to Sam. For abandoning him like something worthless, easily cast off."

"I never-"

Lucifer pinned him with a too level stare (nothing like Sam). "I should be grateful for your part in bringing him to me," he said, voice lowering slightly, going soft and quiet and dangerous. "But if it were up to me, Dean, I would pull you apart piece by piece for a very long time. You're lucky I care too much about Sam for that. But that's the caveat to my offer."

He stood up, smooth and graceful and standing tall like, Dean realized suddenly, Sam hadn't for a long time. "The minute you do something I don't like, something that inconveniences me – you will die. Probably vomiting up your entrails as they liquefy within you. For instance. Just for you, I can be creative." Lucifer smiled, softly. "You should say goodbye to your brother, Dean."

Dean felt cold, inside and outside. It was over, now. Over. "Can I talk to him?" he said, and couldn't believe he'd even asked, couldn't believe how little anger he was feeling and how much…everything else. Lucifer looked briefly amused.

"No," he said, mildly. "Sam is safe right now. He deserves a rest. He doesn't need your blame, your finger-pointing. He's not yours anymore, Dean. He's mine. And I will take good care of him." One more slight pause. "Think about my offer. I expect an answer next time I see you – soon, I hope." Lucifer smiled again, that awful, gentle expression. "I'll see you around, Dean."

Lucifer turned and was gone. The diner didn't vanish. Wake up, Dean willed himself. Wake up, you need to-

He couldn't. (Didn't want to.)

He dropped his head forward and cradled it in his hands.