Speaking as a bi guy here ...
Over the years, I have enjoyed numerous FMF and FFM 3-somes. And a few MMF 3-somes. In any 3-some, I want to connect with both partners, and make sure everyone gets plenty of attention and affection.
I had two MFM encounters. The first was fun, but didn't do much for arousing me. The other guy was nervous about seeing another man nude that close to him and screwing his partner. It was his first 3-some, and I wish he and his partner checked in with each other more and with me about their comfort levels. She really enjoyed taking turns riding both 8-inch poles - but I think she would have enjoyed it more if everyone was comfortable, and the two guys could have coordinated their attention on her. The second MFM 3-some was a non-starter - no sooner did we get going than the other guy opts out. :frown1:
I find it kinda sad that more straight guys don't want MFM sex. I see MFM and MMF 3-somes as a wonderful gift for a woman. It's also an opportunity to bond emotionally with another man even if they don't want to fuck or suck each other. It's also an exciting way to learn ideas and techniques other men. Even if I was straight, I'd still want MFM sex, and if my femalre partners wanted that, I'd happily oblige. Rest assurred, I'd also want plenty of MFF and FMF sex.
From conversations (and from my personal experience), one reason many guys like to see 2 women go at it is because they are thinking "I'd like to fuck both of them!" Just as when a guy sees a picture of a nude woman, he often thinks, "I'd like some time in bed with her!"
I noticed somethings matter more than gender and orientation for any 3-some, 4-some, or more-some. A sense of humor, comfort with one's body, being able to articulate one's feelings and desires in the moment, willingness to be the center of attention graciously, and willingness to yield the spotlight so somebody else can receive pleasure.