I hate to say it, but no one knows. The issue is: are we all “born straight” and then we become gay? Are we born neutral and then develop our sexual orientation? Or are some of us “born gay”? No one seems to know.
I don’t know what caused my homosexuality. People will put forth the same old cliches: Domineering mother, absent father, bad experience with women, molested as a child, etc. None of that applies to me. I know for a fact that I didn’t choose it, however. This will be the 1765th time I’ve said this, but if someone can explain to me how a person can will themselves to be attracted to something they weren’t originally attracted to at as young of an age as 11, by all means, go ahead. Otherwise, there is no legitimacy to the claim that it’s a “choice”.
Homosexuality is abnormal in a technical sense. All “abnormal” means is “not typical”. It says nothing about “bad”. That’s just a product of people’s associations and connotations which are not present in the actual definition of the word.