But monogamy isn't about attraction, someone monogamous doesn't mean they never appreciate another person, it is more about attachment - they're not capable of attaching to more than one person at a time, and not interested in trying. My primary BF is the equivalent of a 0 on the Kinsey scale if one existed for monogamy
He has had the opportunity to flirt, have sex, cheat and more throughout his life and freely in his relationship and hasn't done it. I know he hasn't in our relationship because he has permission and he's even tried to see if it would help his jealousy with me being poly and really, he's just plain mono.
I'm fully in favor of rejecting **** shaming and encouraging openness and honesty, but I'm also not going to assume everyone's lying. Not everyone cheats, nor would poly solve all the relationship problems in the world. In fact, I argue that poly is hard and takes more work than the average mono relationship, although I also think the rewards are greater.