I’m not going to assume your experiences, but I’m a mostly straight guy who’s had both FFM and MMF threesomes while I experimented with polyamory.
I vastly preferred the FFM stuff, because boobies, but I did learn that I can find effeminate men attractive, if I couldn’t it would have never worked. If you’re really a person who can’t interact with someone of the same sex, then I really don’t think a threesome is viable.
I’ve had threesomes end where the other dude just really wasn’t into it, and we all decided to call it off. If everyone isn’t having fun, then no one is.