We've been swinging for 26 years. In the beginning although female bisexuality was common and "normal" neither one of us would have even considered incorporating male bisexuality into our play. But over time my cuckold/sub tendencies began to emerge and we started seeking dominant males to play with. "Forced bisexuality" and subservience on the part of the husband toward the dominant Bull was a somewhat common scenario in that kind of roleplay. As it turned out, my wife becomes very sexually attracted to the Bull after a subservient display by me, My subservience/oral service symbolically transfers the power in the dynamic from husband to Bull and the wife then naturally becomes more attracted to the dominant Alpha Male. That's how we got started and now male bisexuality is just a normal part of our play - even without the cuckold/Bull dynamic.