Since the dawn of time, this character has been strictly heterosexual until one day he meets the man that will change everything. While he’s happily in love with his new partner, he makes a point of saying that this is the only man he’s ever liked and every single other person has definitely been female. This is the only guy he’s ever been “gay for.”
Why this can be bad: Just don’t. Don’t do this. While, yeah, there are definitely people who do come across that “special someone” who doesn’t fit into what they thought their sexuality is, there’s a name for that: bisexual. By having a character say or imply that he’s only “gay” for this one person, you’re contributing to the erasure of the bisexual community. Often times bisexuals are labeled as confused or transitioning, and while there are homosexual people who have used the label as they discover their identity, this is still a very real sexual orientation that is too often glossed over, not mentioned, or wiped under the rug.
How you can fix it: Don’t ever use the words “only gay for you.” Or anything similar. And on top of that, just say the word “bisexual.” Authors, show writers, living breathing humans — all kinds of people seem terrified by this word, as if it’s going to summon a giant queer monster. But I promise: it’s okay.
Bottom Line: Stop erasing bisexual people, and let your characters identify it as it.