I had a sort of MMF one time. Me and my best friend, our bf's and her bf's younger brother were all watching a movie together in her media room, and we'd had a few wine coolers. I was sitting on a big couch between my bf and the "spare" guy, and was making out with my bf. My friend and her bf started doing actual sex on another couch next to ours, and then my bf knelt on the floor between my legs and started fucking me. The other guy pulled out his cock and was stroking it as he watched me and my bf, and his brother and my friend. He took hold of my hand and put it on his cock, and started using it to stroke himself. My bf looked at it, saw what we were doing, and just smiled, so I kept going, and jerked him off.
We never did it again, or did anything else, but it was kind of cool. I don't regret it.
Kim