Hello everybody :)
My delicious is all messed up because of the recent changes, so I ended up losing a lot of links. There's one fic in particular I've been desperately trying to find again...

Sam & Dean, I don't remember if it's Wincest or not. It's set I think right after the season 4 finale. Sam is devastated by what happened and thinks that Dean wants to kill him. They're in the Impala, going to a hotel. When they get there, Dean goes inside to book the room and leaves Sam the gun; Sam thinks Dean wants him to kill himself. As he prepares to do it, Dean comes back and is shocked and horrified and tries to stop him. Sam thinks it's because Dean wants to kill him himself, so he says something along the lines of 'just make it quick', and Dean is horrified when he realizes what Sam thought he wanted.

Thank you for your help!

ETA: found in the comments!