Dean was gone. Dead. Ripped apart by hellhounds right in front of his goddamn face and he didn't do anything why didn't he do anything how couldn't he do anything it was all his fault all his fault he was too slow too stupid too weak he was nothing he is nothing oh god-
The anger, at himself, at Lilith, at everyone, at everything, was so encompassing that for a while he blazed through demons himself going after Lilith, not caring about the monster he knew he was becoming, not caring if he died because at least he'd be where he belonged. With Dean. Oh god, Dean. He was everything Sam had never been. The hero to his monster. The salvation to his tainted, ugly blood. Sam's saving grace, he thought, would be to protect Dean. If he could keep the good brother alive, then maybe that would be the one good thing he did with his life. He'd do almost anything to make Dean happy, but he'd do everything to keep Dean safe.
Then, he'd met Ruby.
And everything went downhill from there.
The demon blood gave him power, but that wasn't what he wanted, wasn't what he cared about. What he cared about was that, even though he was drinking blood, a demon's blood no less, it gave him the ability to save people, and to avenge, maybe even rescue his brother from Hell.
It gave him a second chance at redemption, at doing something to make his life anything other than disappointments and mistakes.
And they were having sex. She acted like she loved him and made him forget everything and that was the best thing because to clear his head these days it took something drastic and at least this worked better than cutting his wrists and she was beautiful and she wasn't sweet she acted like she was in control and that sometimes worried him but what did he have to lose because his brother was gone and she was there and Sam couldn't be alone anymore.
Then Sam wanted more blood and that scared him. Ruby wanted him to drink more and that also scared him. But he did because, again, what did he have to lose?
But sometimes he thinks back to the year before Dean's deal and he wonders what Dean would do and what Dean would think and then he stops thinking that because he needs to focus on Lilith and also he's pretty sure that if he gets Dean back he'll hate Sam and Sam can't handle that.
And then Dean's back and he's pissed about the blood and Sam realizes it's an addiction and he can't stop and did Ruby know? She couldn't have known because she wants Lilith dead too and she can't be tricking him because that means the whole 4 months was a lie and she was using him and she still is and Sam can't handle his brother hating him and this (another) huge screw up.
And then the detox comes and Ruby can't help him now he's dying he has to be dying he wishes he was dying and Ruby doesn't care he needs someone to care he needs someone to understand he can't kill Lilith without this and he has to show Dean he has to show Bobby he has to show that he cared that Dean was in hell he has to show that he can do something important he can do one thing right.

Oh God.
Lucifer is out and he did it and this is the worst one yet.
This is the ultimate fuck up of all fuck ups.
He wants to die but he wanted to do one thing right and now nothing is right and he did all of this and now all these people will die and nothing he will ever do will ever make up for this he's damned he let Lucifer free and he should just fucking die already because all he does is fuck up and-
And Dean leaves him.
Well, really Sam left.
And Dean locked the door when he knocked.
He just wanted to do one thing right.
One thing right.
He was right. This is it. His last good deed.
He leaves Dean a note beside his soon-to-be corpse. The maid who finds him will call the police and the police will hit speed dial one and Dean will get the note and he feels bad about the maid who will find him but he needs to do this.
When Lucifer brings him back he crushes his phone.
He crushes and breaks the pieces.
Dean will be safe from him.
He'll keep trying.
And when he finally says yes, Dean has gotten all the rings and shows up at the graveyard and he knows and its like he and Dean planned this all along until he can't get control and he almost kills Dean and Bobby's dead and Cas is dead and all he can think is last good deed last good deed last good deedlastgooddeedlastgooddeedlastgooddeedlastgooddeedlastgooddeed.
And then he's in the Cage.
"Last good deed, huh? Let's see if it was worth it, what do you think, Sammy?"