Steven Universe - I mean... Technically, they're rocks...

According to all known laws of biology, there is no way a gem should be able to be gay.
It is not an organic lifeform and has no notion of gender.
The gem, of course, is gay anyway.
Because gems don't care what humans think is impossible.

Well I mean, if they have no biological sex, then they technically ALL have one sex, right? Then that'd force them to be only attracted to their own kind, which only has one sex. So technically speaking, yeah they'd be homosexual. I mean, gems who love humans and stuff, that's another story. But yeah… since they mostly call themselves females, I'd say they're almost all gay.