When Sam finally decides he can't take it anymore, he goes to the makeshift kitchen at the cabin that used to belong to Rufus and pours himself a fifth of whiskey, which he downs in less than 5 minutes, then pours another. Stumbling slightly, he makes his way to the bathroom, where he opens the cabinet, takes out every bottle that rattles, and puts them on the counter with the whiskey glass.
Lucifer pops into his vision, sitting on the lid of the toilet, grinning sadistically at Sam like usual. "An overdose." Sam tries to ignore him, but Lucifer continues, "You are such a teenager. Could you be more dramatic?"
"Dean won't let me touch the guns anymore," Sam mutters. "It's better this way."
"Oh my God, are you serious?" Lucifer sneers, straightening up and pressing his hands on the edges of the lid. When Sam ignores him again, he shrugs and says simply, "Have it your way," before disappearing again. Sam breathes a sigh of relief- doing this with Lucifer around would be much harder. He'd probably make the pills look like maggots or something.
Sam looks into the mirror at his own face and sees someone completely different than the Sam who left Stanford seven years ago, or the Sam who cheated death five years ago, or any other version of Sam that ever existed. This Sam is small and broken and terrified; this Sam is tired and waiting for an end.
Sam intends to give himself that end.
About three hours later, Dean still isn't back in the cabin, and most of the bottles are empty. Sam can't function well enough to pour more whiskey into the glass, so he just drinks straight out of the bottle. He's close to the end, and good thing, too, because this is really dragging on far too long for his liking; he hadn't expected the cloudy vision or the inability to stand. Sam is slumped against the wall of the bathroom, opposite of the mirror that he can't see anymore.
A thought flits across the front of his brain- what about Dean? He'll be alone now, but Sam doesn't care; he knows he's being selfish, but wasn't Dean being selfish when he brought him back the first time, wasn't Sam supposed to die when he was 23 anyway? He could've had paradise all those years ago and Dean took it away from him, and look at him now- dirty soul, tainted soul, broken soul, soul of hellfire and demon blood.
None of this would've happened if he'd just died back then; no Ruby, no demon blood, no angels, no apocalypse, no Leviathan, no Lucifer inside his head, no hell-walls breaking, no hell-walls in the first place. Dean could've handled well enough on his own, didn't he do it after the graveyard scene, and for a whole year even?
Part of him knows this isn't true, but he doesn't care, really. Anything to escape Lucifer is good enough for Sam.
His vision is fading fast, and he must be nearly done now. Peace at last, but Sam should know better, because right before he fades completely, Lucifer pops back in, clear as crystal, evil grin all over his face.
"You can't escape me, Sammy!" he says gleefully. "I'll just be on the other side!" Lucifer breaks into laughter, and panic fills Sam's head as his vision fades to black, and he can't die now, not if Lucifer will still be there, and he tries to yell for Dean but he knows it's too weak, too little, too late and there's nothing left.
Dean hears him, and the last thing he hears is the bathroom door slamming open, and Dean's voice yelling "Sam!" into his ear but it's too late for him and he's gone.