They should've nipped it in the bud when they had the chance. They should've stopped it before it got beyond kissing and heavy petting. They should've written it off as a bad mistake. But they didn't, and now it was out of control. And in many ways Sam's fast-growing addiction to Dean was worse and possibly more dangerous than his demon blood addiction.
Sam used his height advantage and the leverage of the wall to shift enough to guide himself to Dean's entrance. In the back of his mind somewhere he was praying he didn't drop Dean, but it was unlikely.
He started to push in, burying his face in the crook of Dean's neck to hide his groans.