Spoilers for 5x04
Sam wakes up, rolls over, and for a moment he doesn't dare open his eyes. He counts to three in his head, bites down hard on his lip, and at last lets one crack open.
His brother is there, in the other bed. Dean's face is lax in sleep, lips parted and chest heaving as he breathes. Sam relaxes.
"We need to talk, Sam."
Sam jumps, bolts upright. Lucifer is sitting at the end of his bed, calm and unflinching. It reminds Sam of Castiel, when they first met. Castiel's unwavering blue stare and blank face.
"Go away," Sam orders, draws his knees to his chest like a child and wraps his arms around them. He feels small again, like the little boy afraid because Daddy hadn't made it home yet.
"I just want to talk. I'm going to tell you a story, Sam," Lucifer turns to look at him, "And all you have to do, is listen."
"Nothing you say can change my answer."
"Do you know," Lucifer asks, "Why I was cast aside?"
Sam nods, "You thought humans were unworthy of God's love. You tempted Eve with the forbidden fruit."
"I loved my father, too much. I loved him, more than anything. I loved him and he asked us to love you, humans, more than we loved him. I couldn't do it. I couldn't love anything more than I loved him. I begged him to understand." Lucifer pauses, stares off into the distance as he remembers a time long forgotten by all else. And then he turns his eyes back to Sam, "But you understand, don't you, Sam."
Sam shakes his head.
"Yes, you do. You understand what it is like to love someone more than you should. To be ready to sin for that love. Willing to fall for that love."
Lucifer drags his eyes from Sam, over to Dean. Sam swallows hard because, yes. He would give anything, anything for Dean, do whatever he asked.
"One day," Lucifer says, "I'm going to ask you. And it's going to be the only way to save him. And you're going to say yes."
Lucifer disappears, leaving Sam alone.
"Sam?" Dean sounds tired and groggy, voice slurring with sleep as he sits up, "Were you talking to someone?"
Sam shakes his head, slow. "Just myself."
He knows, in that moment, that one day… One day, he's going to say yes.
For Dean.