Writing a bisexual character starts with recognizing that their sexuality is just one facet of who they are, not the entirety of their identity. I’ve read so many books where bisexuality is either treated as a plot twist or reduced to stereotypes—like the 'confused' trope or the 'promiscuous' archetype. Instead, think about how their attraction to multiple genders shapes their worldview subtly. Maybe they notice beauty in a wider range of people, or they’ve had to navigate assumptions from both straight and queer circles. A great example is Rosa in 'Brooklyn Nine-Nine'—her bisexuality is casual, unforced, and woven into her humor and relationships.
One pitfall to avoid is making their bisexuality contingent on plot relevance. They shouldn’t 'turn bi' for drama or to serve a love triangle. Let them exist in their fullness, with past relationships, preferences, and quirks that aren’t tied to their sexuality. If you’re unsure, talk to bi folks or read memoirs like 'Bi' by Julia Shaw. Authenticity comes from understanding that bisexuality isn’t a phase or a middle ground—it’s its own rich, valid experience.