Unless you are physically attracted to men (pardon my French, but your dick goes up and you get hard), then you are not gay. But from personal experience, sexuality can change. I used to be straight. And then one day i kissed a man, and from that day on I have only been attracted to men. I don't know why or how, but that's just what happened. It's life.
And btw, being gay is not a bad thing. I thought it was, but now that I have accepted it and come out of my shell, my life has been pretty damn good. So if you are still straight, great for you. But if you turnout to be gay, don't be afraid, because it is a wonderful thing, contrary to what everyone says.