This is an amazing thread. My best friend is bi. We were lovers years ago in college, but broke off the sex when he fell in love with a woman. He said mmf sex is extremely hot, but his wife gets very jealous, maybe because she thinks he will like the other guy more than her. I've never done it with him and her together, or with him and another woman, and only occasionally since they married. For the most part, it is blue balls on both sides when we are together. I guess he's my edging buddy, rather than a fuck buddy.
But I'm amazed at how many of you do this, or fantasize about it. It guess it makes sense, since men definitely like competition, even in sex. But the women who are able to do this must be unusually confident of both themselves and their guys.
Or maybe this works only with guys who are emotionally straight. You have to be able to love guys in order to have a best friend, and you have to be unthreatened by guys to have sex of any kind with them, casual or emotional, but you must have to be able to compartmentalize things pretty well to do this. If guys were really at risk for falling in love with other guys, this kind of thing would be more threatening than enjoyable, I think.
Maybe it's this competition factor that makes guys like watching porn so much. You feel like you're in competition with the guy on screen fucking the girl you want to fuck, which turns up the heat.