Hey Nyc, thanks for working through it with us. I totally get that you're not in any way homophobic in your daily life, and I'm not saying you need to fight your personal preferences, but yeah, it remains hard to understand "bi = less masculine" as being not about some kind of prejudice or misconception about gay/bi guys. The competition part makes more sense in the abstract, though I still have a hard time grasping it on a personal level.
I think the best analogy would be if you were to ask if a straight man might be considered homophobic if he lost interest in a woman after learning she was bi. And to be honest, yeah, I would be pretty pissed off and would have a hard time understanding it as anything other than prejudice if a man expressed an attraction to me and then backed off once he learned I like women as well as men. It *would* kinda be better if he'd never been attracted to me at all, because then it wouldn't be solely about him rejecting this one, integral part of my identity, which our culture as a whole is going into such convulsions over lately.
It's much harder to make an equivalent comparison to a gay person, male or female, not wanting to date bi people, because there's not the same cultural bias against opposite-sex attraction that they'd be playing into. I would still be annoyed at the hypothetical gay person on a personal level, and might question if they had misconceptions about bi people, but I wouldn't tend to chalk it up to some kind of "straight-phobia", y'know?
Me, 30ish bi female, been doing solo poly for roughly 5 years. Gia, Clay, and Pike, my partners. Davis, ex/friend/"it's complicated." Eric, Gia's husband. Bee, Gia and Eric's toddler.