Reading your original post, I bet you have one of two things going on here.
Either you got ahold of a woman-hating jerk who really just wants to have the adoration of NRE from as many women as possible.
Or you have a genuinely poly man who has been indoctrinated to believe that having multiple loves is impossible and/or immoral.
Actually, it could also be both of these problems.
Either way, it is probably a deep seeded fact of his psychology. You're not likely to change him.
I have to tell clients all the time "if you dont like him just the way he is, don't stay with him. Men don't (usually) change"
- All my Love.