A lot of the search for a gay gene seems trapped in an outdated understanding of sexuality as a binary proposition: "you're either A or B." How do you even begin to contemplate a study on sexuality once you understand it as highly varied and fluid? Same with gender. They're bimodal distributions at best . You can't just crop off the confounding valleys and call what you do with them good science.
I am gay, and I have been since I hit puberty. It's completely stable, a fixed personality trait my whole life. It's so... exact. That one little thing, completely inverted from a good majority of men. It's like someone flipped one little switch, that affected only that, at least as far as I can tell.
Bisexuality or pansexuality or whatever you want to call it, on the other hand, seems to fit many of the proposed origins, far better than exclusive homosexuality would. E.g., fuzzy pattern matching gone awry for finding a suitable mate, triggering a bunch of false matches. But it's not like that. It's very precise. That has always struck me as ever so strange.