My Girlfriend and I have had threesomes with two different lady friends. The first one was one of my guy friend's flat mates, worked out fine, stayed friends with her for many years. The second was a girl I'd met at University, My girlfriend and I have fucked her on two occasions actually, and its funny, I feel like Girl 2 is closer with my girlfriend these days (they meet up more often), although we're all still close friends and we even hang out with her current boyfriend.

Anyhow a year ago I kind of completed the circle so to speak. I had a threesome with girl 1 and girl 2 without my girlfriend. The problem was, girl 1 had gotten engaged. I felt really bad after the fact but I think at the time, I went with it because A) I'm heavily intoxicated B) Its two sexy women wanting to fuck you C) Girl 1 kept complaining about how boring her Fiance was so I figured, fuck it; sounds like that relationship is destined for the rocks.

I really thought girl 2's engagement would be called off, looks like she chose to stay with him. Girl 1 married her fiance a few months ago, I haven't spoken to her since the night we fucked. I left a voice message to see if she got home okay, I missed her call and she left a brief message on my phone saying she was fine. I think she sounded guilty as hell. Girl 2 was fine with it, she'd only just met Girl 1 but she felt a bit bad for her. My girlfriend was also fine with it, found it amusing for the most part. I regret losing that friend but people make choices and move on. Nothing can be helped.

TL;DR If everyone is on the same wavelength and you keep things fun, it is entirely possible to have sexual history with friends. If cheating is involved, it can potentially ruin things.