I have never in my life seen someone give a good reason for not dating a bisexual person. It almost always boils down to “they cheat” or “they’ll leave me for a guy/girl”. For lesbian and gay people, the reason usually boils down to “ew they had sex with a guy/girl”. Straight girls who won’t date bi guys usually pull out the “he’s on the DL” mess. People love pulling the “personal choice” card, but if you press them the biphobia always comes out.
I particularly don’t like the “they’ll leave me for a guy/girl” bit. It’s always rubbed me the wrong way. You know what? Maybe they’re leaving your raggedy ass for being a biphobic piece of shit. Maybe the got tired of hearing biphobic bullshit every time they were around you and decided to be with someone who gave a fuck about them. Maybe the problem is your ass and not them and their sexuality.
Maybe you need to fucking question why the gender of your ex’s new boo bothers you so fucking much. They are not with you anymore! The gender of the person they’re currently with has not a damn thing to do with you! Mind your own business! If you’re so concerned about who an ex-partner is with, you’re probably an extremely intrusive human being or you’re hung up on the past relationship which they’ve obviously gotten over.
The “they’ve touched a pair of genitals I don’t like” mess makes me see red. If you’re a lesbian who believe that a bi woman who has touched a dick before is “tainted”, you have some shit you gotta work through. Same goes for gay men. Thinking a bi man is “tainted” because he’s touched vagina before is something you need work through with someone. The main thing you should discuss is your transphobia.
Here’s the thing, some women have penises and some men have vaginas. It’s entirely possible to have been in relationships with only women and still have dealt with a penis. It’s entirely possible to have been in relationships with only men and still have dealt with a vagina. It’s also possible for women who have dealt with cis men’s penises to be attracted and want to enter relationships with women. The same goes for men and cis women’s vaginas. There’s nothing disgusting about handling more than one set of genitals.
If you honestly believe there’s something wrong with that, you have work to do. You are the problem, not the bisexual person in question. You have layers of bullshit you gotta work through. Yes you are biphobic and yes you are most likely transphobic as all hell too. You need to work on you before you enter any relationship.