I remember a particular scene: Dean keeps getting flashes of a memory. In it Dean has decided to visit Sam at Stanford-I don't remember if he just wanted to see him or if he decided it was actually time to go talk to him (though that doesn't happen). Sam is playing soccer or football or something and has taken off his shirt. In the flashes Dean focuses on different things: he sees the sun shine off the Impala or off Sam's body  (his sweat?) and Sam had dirt on him.Eventually Dean sees the whole memory and feels the arousal he felt watching Sam. This was the first time he felt something like that. He drove off and repressed it so much he didn't even remember it happened.   

So over the course of the fic Dean remembers. I think it is set in season 1. I'm pretty sure it was Sam/Dean eventually. And it was a long-fic.  I have some ideas, but this is one scene/theme so it would take me a while to be sure I had the right story.

Thanks anyone who replies!!