Well, I never want to question other people’s kinks, or pass judgement on them because of what they like.
I can say, personally, is that I do see the sexiness in overwhelming a woman in any way you can – with toys such as a Hitachi, or another woman in a FFM situation, and yes – MMF, too but there is a caveat with any threesome for me.
Personally, I am not one to share when I develop feelings for somebody, and I don’t expect the woman to share me either.
The truth is – you should seek out advice from other people who have had threesomes – in their relationships. They can provide real first-hand advice on having lived through it, hindsight and lessons learned, etc.
From what I found in my conversations, most the time – though not all the time – it doesn’t go well unless all three parties are not emotionally connected in a relationship together. Just three people having fun, fucking around. That is the best way, from what I hear.
Usually, jealousy sinks in and it is just a matter of time before the relationship dies. Most times – it goes like this: guy convinces girl to have threesome, she folds like a deck of cards because she loves him and enjoys being kinky, goes through with it, the other girl feels awkward because the girlfriend/wife cries at some point, and then the resentment sets in, the gf/wife torments him, and they end it eventually.
Fuck that. I’d rather just not bother.
The fact that your boyfriend wants a guy to be his accomplice is not really relevant. In a friend-only situation, I would totally be down for that too, because it is hot to see a woman overwhelmed. But no – male-male action would be part of it for me. I am not a homophobe so some accidental ball slapping would never really matter to me; I would be more focused on the woman getting lost in space. I am just not going to be intimate with another man directly.
However – one part of your ask is a bit concerning to me and may be telling. The part where you say “…the guy and I dominating him. He’s very flexible with his sexuality, and he isn’t attracted to men at all” leads me to believe you are probably trying to convince yourself he is not bisexual or gay, when “him being dominated by another man” is likely a sign he likes men to some degree.
The stigma that comes with homosexuality makes me cringe; so many people do their best to shield who they are inside to not deal with in fear of the opinions of the dumbest sector of our society anyways, when once they finally embrace it, they almost always end up happier individuals, being free of hiding who they are inside. Maybe he is bi. Maybe I don’t know shit about him, and I am reading into your words wrong, but I suspect I am probably right to some degree, if he wants to be dominated by another man.
I am 100% straight, so I can tell you what it is like from the perspective of a straight man. We do not want to be sexual in any way with another man directly – that is kind of the definition of being gay or bi. To be intimate, sexually, with a person of your own gender.
If that is the case, I suggest you get to know your man a little better and really find out if he is not closeted, bisexual, gay, or whatever. There are lots of stories about women who fall in love with men who are just not ready to come out yet; you don’t want to be falling in love with somebody who is unavailable to you in the sense you need over the long haul.
You may find you just found a friend for life though, as you help him navigate this very confusing time in his life. Who knows.
Just my two cents though.