I think this is spot on! I've never understood why bisexual people are supposedly more likely to cheat on their partner than straight people. If both of you guys had been gay, his dating you would not have done anything to reduce the presence of other gay men in your life, some of whom might be very attractive and might be attracted to you.
But you're only likely to cheat with women? How does that work even in theory? I don't get it. Never have.
The best way to educate folks out of these attitudes is to talk about it openly.
So thanks for the story!