its hard to write a bi character and most people go off there own experiences, not saying its universally true but the few people i know who are openly bi actually fit that stereotype, I have actually asked and all 3 say the same thing "feels good why do i care" go off what you know i guess
I don't think it's especially hard to write bi characters.
It is not easy to write good characters because you have to strike a balance between being unique and being a stereotype people can understand and/or identify with. And you have to do that with limited lines and screen time.
From my experience, people are people, no matter what their gender or sexuality may be. Some are hilariously awkward when flirting, some are very direct, some are suave... but that has nothing to do with their sexuality.
I don't see why a character needs to be treated differently because they are bi. It is not like their personality changes because of it.