It is biphobia. You using yourself being a bi person as to excuse gay people for things you'd never forgive a straight person for is the same branch of reasoning as a man trying to explain away a woman sexually assaulting a man by arguing that women in general have it rougher and that he, as a man, wouldn't mind it so no other man should either.
When you’re in a country where being in a same sex relationship is heavily stigmatised like in Japan, obviously you’re gonna be scared to end up as a person’s experiment before they ‘settle down and have kids’. You can’t deny that many bi people in a lot of Asian countries CHOOSE to be heterosexual at the end not because of their true feelings but because of the social stigma that they might face. So obviously what the bottom showed was not real biphobia but a kind of a trauma response after getting hurt by an asshole bi man who intentionally hurt and cheated on him to chase the ‘normal’ life.

too many of you lot are like "bleeegh there's biphobia", acting as if Naoki doesn't have a 1000% valid reason to lowkey freak out about the idea of dating someone who's never been in a queer relationship before, shit I feel like most queer people fucking HATE the idea of potentially being an experiment for someone. also before any of you try it I'm literally bi.