i've had threesomes with two different couples... the first one was with a mate and one of my ex-shags... it was okay, we did it only once and nothing bad has come of it, me and him are still good mates and me and her still hardly talk
i've also had one with a married couple, this time its a bit more involved as we've had it quite a few times... its all stopped at the moment because they're having troubles between themselves and i'm unsure if they stem from having the threesomes...

hopefully not though. we've all grown really close because of it.
never had it FFM, but would love to give it a go