I read this story a long time ago (years I think) so what I can remember is this...

Dean is cursed and doesn't remember that Sam is his brother. The boys go back to Bobby's house to try and fix the curse. At one point Dean offers Sam some kind of meat (a burger maybe?), but Sam refuses and when Dean asks why Sam said he'd know why if he remembered Sam at all. I think this comes from when Sam was tortured by his cousins and one of them tried to literally eat him and he still has the bite marks from it.

I also think Dean didn't really want to remember he had a little brother all that much because he liked being an only child.

This may or may not be me mixing two stories together, so if any of this sounds familiar let me know. Thanks guys!