This one felt ok to me, because by doubling Dean, it emphasizes Sam's love/desire for him. It also served an actual purpose, emotionally and psychologically, for FutureDean. By being with this Sam, and seeing how tender and loving he was with his Dean, it broke down some of his walls. And Sam was able to give him a key to getting his Sam back. None of that would have been possible were it not for the three of them actually being physically intimate. It could not have happened in a conversation. FutureDean couldn't help his feelings coming out, even as he tried to be hard and "yeah, you little slut"... he had to whisper "You're mine" and had to touch Sam gently.

In my verse, the main reason why FutureDean turns out the way he does is because he and Sam did not reconcile after a big rift and they don't have each other in the full romantic/sexual way like our Sam and Dean do. :) So this ficlet is FutureDean sent back after the rift, before Sam says yes to Lucifer.