Gay men are interested in romantic and sexual relationships only with other men. You don't say whether or not you are interested in girls. If you are, then that's definitive... you definitely aren't gay. If are primarily interested in girls, but you would consider having a sexual relationship with a guy, then you may be bisexual.
Lots of straight guys actually do watch gay porn. It prominently features penises and male enjoyment (unlike straight porn which tends to focus on the girl), and since you know from personal experience how great all that feels, it's natural to enjoy watching it happen on screen. Plus straight and "lesbian" porn is usually so fake I'm not sure why people would enjoy it anyway... lol...
Anyway, your porn preferences don't determine your orientation; your real life preferences do. Even if you are sexually interested in both men and women, but *prefer* to identify as straight and date only women... that's fine! It's a free country - you get to pick your own label!
I'm a bisexual chick, and I sometimes watch gay male porn... so far it hasn't turned me into a gay man! =P