So here's my opinion: If a man has a female partner and has some form of sex (hand job, oral, anal...) with another man while with his straight partner. And she does not know about it... He is a cheater. That is the crux of this issue no? That's the elephant in the room. I would add this to the guys that get online and stroke with other guys if the partner is not aware of it. That is still cheating no? So because of this truth, many like to say "bi-curious" "mostly straight", or a host of other names. It's tough to admit one is not being truthful. I know it is for me. Sexual behavior ebbs and flows in ones life. I know mine has. So yes, I am a cheating bisexual because of my actions. And this is a forum about sexuality. Cheating is a separate issue. Yes, a large number of bi folks are in straight relationships and cheating with men. But that does not mean we don't have opinions about our sexuality does it?
But this all said, if you remove the cheating aspect of it... I believe there are various flavors of bisexuality regardless of the infidelity aspect.