Does it mean I am gay if........?

I'm 20, currently with a girl, get aroused around her pretty easily, etc. I was curious and watched a gay flick and I was aroused! I got hard to it, however the back-door action wasn't for me and I turned it off. Does this mean I am gay if I got arousal to the first parts? I really like this girl and we get along so well, I really would hate to have to tell her I am gay. I mean some times when I'm around her it's hard for me to hide my ----r in my pants when she is touching me and being all close !