I think the fandom can turn you gay, or make you realize about it OR a lot of people are actually not 100% sure about their sexuality
I don't think people can turn gay (or bi.)
I'm not too sure how it would be for 100% gay people, I'm guessing they would be able to realize it early on since they would be having attraction towards other people of the same gender pretty much exclusively; it would be difficult to think you were 100% straight if you only felt attraction towards people of the same gender as you.
But as far as being bi goes, well of course there's going to be people who realized it early on too and accepted it, but as far as I'm concerned, I was attracted to members of the opposite gender, but I also had... thoughts... as far as people of the same gender are concerned, but I would quickly dismiss those thoughts. It took for me to get a crush on someone I thought was a girl, but turned out to be a guy for me to really come to terms with it and accept it.
It's not that I felt it was wrong, it's more complicated than that and I'm not sure I would be able to explain it. I think maybe it's because people tend to hate on gay people just because they're different, so I didn't want to accept the possibility of me also being attracted to people of the same gender.
I was feeling pretty uneasy when I had no choice but to reconsider my orientation, but really, at the end of the day, straight, bi or gay, it doesn't change anything. It doesn't affect your ability to be successful in life, doesn't affect your ability to do anything. The only difference is that you may or may not end up being with somebody of the same gender as you are, and if people aren't okay with that, then they should just mind their own lives because it really doesn't hurt anybody.