Originally Posted by Halcyon

I never have.

10 years ago, at a rave, a woman licked my back and my gf was furious. But that's it.

My feeling is:
Either establish open boundaries with whatever stipulations work for you.
OR
If you are going to stray, call your girls cell and break up first...no matter what time. Betraying someone you once (or still) cared about is a fucked up thing to do to someone's long term psyche.