my husband isn't bi and he's not "into" my bf in ANYWAY either.
It is QUITE possible to have a 3some with a person you aren't interested in if they aren't the center of attention. In younger years I had two men. They were NOT interested in each other AT ALL. But they knew I was interested in both of them.
They took the opportunity to tease and pleasure me. They never touched one another AT ALL, not even on accident on the hand or anything.
They "split up the body" in quarters and agreed that they would remain in only two quarters at a time (each) and never the two to meet.
"Love As Thou Wilt"