Responses
my thoughts exactlyyyy, they kept going around in circles when they clearly could have mentioned that nozume is simply bi.
the old japanese gay community has their own terms from what I know, they even have a word for a "straight" man who sleeps with gay men, but I don't know why the use of the word bisexual is not common as that, since they are basically the same.
most modern yaois already use the word bisexual tho. I don't know, leave it to us to make free interpretation
"if I'd be born gay, would he have said 'yes' to being my boyfriend from the start?" this seems like reflections of a bisexual experiencing biphobia within his own community. your boyfriend doesn't believe you will stay with him because you were with the opposite gender before him.
just to add: I know there is significant experience among lesbians and gay men about being left by their partners because of heteronormativity. however, this painful experience can translate into biphobia in many cases, which ends up hurting all parties.
the manga does not use the more accurate phrases because for some reason some yaois are allergic to the word "bisexual", perhaps based on the old japanese gay community, which only acknowledge gays and straights