I met someone who for a time was an ex-heterosexual. Or more precisely he'd changed from a heterosexual to an asexual being.

He was on medication at the time.

However, there are other circumstances which can permanently change your brain or endocrine system in such a way that your previous sexual attraction and your current sexual attraction are totally different.

Most of these circumstances have to do with illness, injury, or old age.

Among this group of people, there are some who were previously gay.

Those people are truly ex-gay.

Technically speaking, I and most other people are ex-asexuals. Until I was I dunno about 10 or so I had no sexual interest in anyone. Then something changed. I started to look at a certain age and gender group in a totally new light.