Yeah, if its not your thing, then it's not, don't try forcing things, that never works out well.
But a Bi MMF threesome is a great way to ease into it if your curious, I'm guilty of helping a few guys with their first times experimenting with men.
And I'll be honest, some it just isn't for, most have loved it. But if your nervous, you will clench, then pain, then no fun, so like you said, you loosen up first, not just physically but mentally.
Few drinks, play with her, get turned on, then if you want to be bottom, let him start on you while your on her, (just touching, fingers, so on). slow, go slow. It's not a race. You will know when your ready for more, then he can taken the next step.
Most MMF threesomes we have are about 4 hour sessions, yet 1 on 1 sex is what, 15 min, an hour max?
Both me and my husband are basically, eyes face, and for me bum, for him, boobs.
Nothing else for me I think, I like deep voices, but more so, I find high pitched and scratchy voices a turn off.
But then him, being outwitted. He is stupidly smart, he has a PhD and 2 Masters, and finds someone outwitting him or outsmarting him actually a turn on. It's weird. The odd times I do it, prove him wrong, he almost instantly jumps my bones, he can't control himself.