Funny enough, you asked this question not long after I answered someone else’s concern about there being a stigma towards bisexuality in the gay community. Perhaps reading my response to that one here will provide some insight from the other side.
If you have bi friends, then I doubt the struggle is you being bi-phobic. I don’t think your root problem is that he is bi. I think your root problem is that you are feeling jealous. And the fact that he is also attracted to women triggers that jealousy in a new way.
To some degree it makes sense. With men, you have the same kind of equipment to keep your guy interested. With women, you don’t have that luxury. Regardless of the reason, jealousy is an awful human emotional that serves no useful purpose and only causes damage to the relationship. There’s a reason you never hear someone say, “Oh, I just wish I could find a nice jealous guy.” It’s not fun when someone gets angry at you for thinking others are attractive or feeling flattered when others think you’re attractive. And it’s hardly ever a two-way street either.
Jealousy is not about the person we are dating. It is about ourselves and our own insecurities. I am betting that, if the guy you dated said he no longer found women attractive, the root problem would probably rear its ugly head in some other way. So, don’t worry about what he does that makes you uncomfortable, worry about why you are uncomfortable by what he does. Does that make sense?
If you are insecure or feeling overly jealous instead of just happy and excited to meet a guy who also happens to have positive experiences with women, then I would recommend getting a GOOD therapist to work through this stuff. People always whine that therapy is expensive. But honestly, what kind of price tag could you put on feeling more at peace with yourself and the world around you? But I emphasize “good” therapist because a bad therapist obviously won’t get you far. If you don’t feel like you’re making progress with one, ditch them and find another.
Best of luck in dating.