@Trix In my experience with Japanese content, bisexuals are mostly perverted straight. Otherwise, I simply cannot explain why so many manga and LNs refer to bisexual interaction as "perverted tendencies". But that's if you are not one of the authors who think that people can "become" gay or "turn" back to straight depending on the situation. Thanks to this, there was even such a trope as "rape and change of team", so often the manga abused it.
@urtoast Probably yes. As I understand it, she assumed that after sex they might call each other by their first names as lovers or sex friends, but MC stopped that.