As a gay person myself I'd have to say so many youth these day, where I'm from pretend to be gay for attention (its sickening, insulting etc) but it does occur in most mammals, enviromental factors may play a role, im no biologist but I definitely know for most people who still identify as gay, bi or lesbian past 25 its probably a mix of genetics and enviromental factos
Homosexuality has been reported in hundreds of species. I don't think most species follow the social norms. People have been gay since the beginning of time, also. A lot of people in Ancient Egypt were bisexual. It's completely natural. But why should it matter to you? Let the homosexuals be and live your own life. They aren't affecting you in any way.
I personally think that homosexuality is a social phenomena. You are not born to like the same sex. You are born just like every person out there and learn these things through media and social things. I'm not saying it's wrong, but it is definitely a learned behavior and not something born to us.