Books don't make people gay. Attractive people of the same sex make you gay.
Well, that, and what I assume is a brain development process before or during puberty that I don't completely understand but I know has to exist, because I don't remember making a concious effort to be attracted to legs and striking eyes, but I sure am. I bet there is a rabbit hole where I could learn about all this.
You mention before puberty, but the research is quite fascinating. There is strong evidence a hormone imbalance in your mother when your are still a fetus can have a dramatic effect on your sexual orientation as an adult. But also on a negative side sexual abuse of adolescents can also have a significant effect on adult sexuality. Human sexual orientation and the factors at play are very diverse and interesting.
Human sexual orientation and the factors at play are very diverse and interesting.
I know! So interesting, but some people make you feel like a pervert for being interested in it. I just want to know how it works, like literally everything else.