Yes my g/f and I have had 3somes. Mind you, we don't do them all the time, just when we're both in the mood for it. We do FFM and not MMF, not because I don't want them, that wouldn't be fare, but because that type of 3some doesn't turn her on. She likes it when a hot woman fucks her and she likes to watch me fuck another woman.
We do have a few rules though. No firends or anyone we know, only if we're both in the mood for it, on occasion, usually happens when we're on vacation.