Just because you’re writing about bisexuality in a science fiction and fantasy context doesn’t mean you have to use the word explicitly. “Bisexuality” comes to us via a Victorian context of medicalization and psychoanalysis. If we can imagine dragons, we can imagine worlds where that never happened. Some examples:
Ancillary Justice and Ancillary Sword: From the perspective of the cyborg protagonist, gender is an uncivilized social convention. As such, sexual relationships are defined more by the ways in which they do or do not involve the caste system of her (self-applied pronoun) culture.
Door into Ocean: Primarily a mono-gendered and mono-sexual culture. However male outsiders are absorbed into the primary culture of Shorah.
The Broken Kingdoms and The Kingdom of the Gods: Nahadoth’s gender-fluidity is clearly described, as is the triad sexuality among Nahadoth, Itempas, and Yeine.
The Mirror Empire: Describes a five-gendered cultured with polyamorous relationships across all five genders.
An SF&F work doesn’t have to use the words gay, lesbian, or bisexual in order to provide us with radical visions of those realities.