I mean, sexuality sort of changes. You start as a child with no sense of romantic or sexual attraction and then you develop attraction to whatever subset of people as you reach and progress through puberty. But it is infinitely more likely that you will be confused about your attraction than have it actually change. I know that I was in a fake middle school relationship with a girl because I didn't know shit at the time, I was just emulating what I saw adults do and did what I thought was appropriate. I wasn't straight and later turned gay, I just hadn't been able to tell the difference between being good friends with someone and wanting to be in a relationship with them yet.

So later on, when I actually did feel distinct feelings of sexual attraction exclusively toward men, I was able to accurately call myself gay. I'm not sure if anyone ever can change their sexuality or if they can only realize what it is after some level of confusion