I like what this guy has to say about sex, gender and identity:
So by this point it should be plain that I don’t accept the contemporary uses of the term “gender” over and against “sex.” In fact, “gender” is a linguistic term, something for words, words which lack “sex” altogether. “Sex,” on the other hand is directly related to our human reproductive organs, and we live all of our lives as sexual persons, as men on the one hand and women on the other. And one does not even have to “have sex” to be sexual. Such is the fallacy of our day. Again “asexual” is a term which actually means “having no sexual organs.” It does not mean virginity, nor does it mean a platonic relationship. If you want to know your sexuality, you should just take a look. You are either male or female.
This relates to the categories of “heterosexual” and “homosexual” quite directly. Those terms are of very late vintage and they presume that humans are more or less chemically-determined to inevitably and incontestably act in certain ways. It’s founded on a base-level materialism, but one, strangely, not connected to natural law.