Best friend slept with girl of my dreams, what SHOULD I do?

[kazana]

Dude, it's up to you which standards you set for your friends to meet. If they don't, move on.

As for what went down, I wouldn't expect a good friend of mine to do that without at least asking for the go-ahead ("She wants to jump me, doesn't want you. Mind if I proceed?"). Might sound girlish to expect that, but that's what I'd do if the roles were reversed.