When I was 10-15 I was into boys and girls but I already then had a clear tendency to boys. Then with 15 I totally fell in love with a guy and I kinda decided that boys are so much better than girls and from that day on I was gay…

... until I was like 23. Back then I was surrounded with girls and even though I was in a relationship with a boy at that time I started to get interresested in girls. And then I actually fell in love with a girl. Even though it did not work out with her I got excited to know how it is to be with a girl.

Then I started to go to University and there were really many hot boys around me. And the straight side around me totally vanished for like 3 years. At that point a girl seduced me(even with guys I usually was more the seducer) and I was in a relationship with her for about 2 years.

Now that it has ended I think really badly about girls.

Right now I am really happy that i am attracted to guys and I can just choose to be gay.

Edit: My opinion on the matter:

I think people mostly get influenced by the people they meet and fall in love with for the first time. I know a guy who has like a perfect character and even though he is not my type (he is not ugly, but he is just a little bit too hunkish for my taste) I feel a little bit attracted to him.

And the other thing is: If you only meet one gender all day long I think it is just a matter of time until you find yourself attracted to that gender.