Your friends are or were most likely bi-sexual.
“Bisexual” and “homosexual” are made-up terms for the purposes of forming a class.
No one is born one way or the other; sexuality is socialized behavior, subject to environmental influences. Theoretically we could all be taught to be one way or the other (and there are societies, e.g., ancient Greece, where this was the case). My friends were socialized to be heterosexuals but open to experimentation. They weren’t born “bisexual,” “heterosexual” or otherwise. They switched from one socialized preference to another; but for the acceptance of homosexuality and a more welcoming society, these guys would not be practicing homosexuals today.