From my perspective at least, perhaps the important thing here is to consider that, nowadays, we don't tend to think of sexual orientation as being either / or... either you're attracted to members of the opposite gender or you're attracted to members of your own gender (whatever your own gender identity happens to be.) We tend to think of sexual orientation as being more on a continuum with completely heterosexual at one end & gay / lesbian at the other. And in between there are resting places for all sorts of sexual orientation combinations. (At least that's the way I think about it.)

If we were honest many of us, if not most, would fall somewhere in between the two polar opposites on the sexual orientation continuum. So perhaps the enjoyment you're experiencing watching lesbian porn suggests there is some portion of your psyche that is in fact attracted to members of your own gender? That doesn't make you lesbian necessarily though, at least not in my book. That just makes you "normal". Whatever that is...

One thing one does have to keep in mind though is that viewing internet porn can, over time, have a negative effect on one's ability to enjoy the real thing. Here's a link to an article, from PC's archives, on the subject:

How Pornography Can Hurt Your Sex Life