i don't like it much either, but sometimes ppl just don't like to label their sexualities, yk? it's w/e.
(i think the best bi rep i've seen in a yaoi though, is in fake: http://www.mangago.zone/read-manga/fake/
the character even mentions it himself: http://www.mangago.zone/read-manga/fake/mf/v01/c002.2/3/)
aww don't be sorry for being curious!!! From what I know, Bisexual is being attracted to both men and women, Pansexual, however, is being attracted to the person, regardless of their gender.
I know it's kinda confusing but basically, when you're bisexual, you know you like men and women but if you're pansexual, you don't care about their gender BUT that doesn't mean you like ALL people.
I hope that my explanation makes sense, and if you're still confused, you can try searching for more in depth explanations because I'm not really that knowledgeable about genders.
Am I the only one who hates the "I'm not gay but you're special" thing that happens so often. Like it pisses me off for some reason. Does bisexual people not exist in yaoi?? If you're attracted to a girl before and then realise you're also attracted to a guy you are bi. I doubt you can be "straight but will marry this guy I just met cuz he's s P E C I a L" ahhhh