Your friends are wrong. You know who you are attracted to BEFORE you begin having sex. Did you ask them: "Well, if you have never been with a man, how do you know you are not gay, too?" No one would ask that of a straight person. You just "know." I knew when I was 5. I have never been with someone of the opposite sex because I know I don't want to be. I'm gay. I'm happy. I'm in a relationship. Your friends are the ones with the problem-- not you. If they care about you, they will accept you.