Okay, so this what I remember: Lucifer had possessed Sam and Sam didn't manage to take control, so sort of an endverse vibe, but Dean wasn't a rebel leader. Lucifer was keeping him around in like a nice house where he had access to the Impala etc. Dean was relatively content or at least resigned because he wasn't getting tortured and he wasn't dead, so he could probably live with having demons around and it being the apocalypse and all, but he really misses Sam.

So it turns out then that Lucifer was keeping Dean around because he wanted to fuck him. He promised he would let Sam out if Dean did so, so Dean agreed reluctantly, and they did the do, and Dean did indeed get to see Sam for like...a few hours. Lucifer let Sam out immediately afterwards, while they were still in bed together and Dean was naked and humiliated, but ofc, he really wanted to see Sam so he didn't protest. I don't think there was wincest but there might have been. The fic ended with Dean thinking something along the lines of now he has everything he needs bc he gets to see his brother sometimes, I think?

It was a oneshot, less than 10k words. Also, the fic was written in second person so it was quite distinctive. I'm 90% sure I read it on AO3. It's possible it got deleted, but either way I would like to know so I can stop going crazy over it, lol. Thank you!