We don't have gay animals. We have animals that sometimes have same-sex "sex." If there were anything real called "sexuality," then I have three lesbian ducks. Every morning they get in the pond and fuck. It turns out that when a male isn't around (maybe even if there is, we haven't had one), it's literally how they determine their pecking order. My female dogs will also do the same - hump each other for dominance.

There is no evidence of anything considered a "sexual orientation" in animals despite the appearance of "gay" sex, there are no "gay" animals.

I'm actually inclined to agree with all of that, but its a semantic point. There are still animals that do same-sex sex, and animals that dont, if you changed the wording of my comment it wouldn't change the substance of my argument.

*Edited to add, that human sexuality is known to be fluid and changes. That's a fact.

It can change, but not everyones will, just how fluid this situation is for everyone is pretty debatable, and you just said there isn't such thing as sexuality, I don't see a particularly compelling reason your arguments wouldn't apply to human animals if you are going to apply this categorically