(I'm resubmitting this because I realized I didn't put down that I am an adult woman, which will probably affect the votes)
When I am having sex, or masturbating, the only way I can get the first orgasm off is to think of two guys together, usually with a little bondage thrown in.
From what I can tell you're not just normal, you're mainstream! I wouldn't worry at all.
You can go ahead and think this, but you should probably never tell any man that you are with, EVER. If he is like the majority of straight men he will be totally repulsed. Also he will probably be turned off at the thought of you being turned ON, because he will also be thinking of homoerotic scenes.
PS Keep your lesbian porn to yourself, as well. If your gf finds it on your hard drive, I hope she deletes it and dumps you.