Am i gay for this?

I'm 20 years old and I have a girlfriend who i haven't seen for more than 8 months, but i'm staying committed to her and not having sex with anyone, so pornography has been my go-to thing to fullfill my sexual desires.

I have no problem against homosexuals or anything, (my good friend Jacob is gay) but I come across gay porn when i'm on the sites and i get off to it whenever i masturbate to it,

I know in my head that I wouldn't do anything with a guy, but I keep wondering why I would masturbate to it?

Could it be because i haven't had intercourse with anyone for more than a year?

I keep stressing over it and it's bothering me.
I talked to my girlfriend about it, and she tells me it's ok, if i know i'm not gay then i'm not, that maybe it's because i haven't been laid in a long time.

I even test myself, like when i'm not "in the mood" i'll think about doing something with another guy or a picture of another guy and i won't even get an erection, but when i think of my girlfriend, have phone relations with her, or look at pictures of girls then i'm instantly in the mood.