I'm a straight female..why do I masturbate to girls?

I'm straight and have been dating guys my whole life. I am not attracted to women like that. However, when I masturbate to porn, I always look at the girls or try and find a really sexy girl to masturbate to. Does this make me actually a lesbian? Not that there's anything wrong with lesbians or gay people but I have a bf and don't see women in that way but I love watching girls in porn.