What is going on with me... am I bi?

I seriously have no idea what's going on in my mind but I'm really scared of an ashamed by it. I don't want to be lesbian, and I don't want to be bi. I have nothing against people who are at all, that's great for them but it's not for me. I've been with my boyfriend for 3 years and I love him, I find him extremely attractive and really love sex with him. He turns me on a lot. But, for some reason, I find myself getting turned on by girls bodies in porn, and the thought of oral with a girl turns me on too even though I really don't want it to. For some reason when my boyfriend eats me out I don't get as turned on as I do when I think about a girl eating me out, which is embarrassing to say. I would never want to kiss a girl and I wouldn't want to be in a relationship with one so I really don't understand what's up. I never see a girl out in real life and think "oh, she's hot" or check her out or something. It only seems to be pictures/videos.

I'm still 18 so is it just hormones or something? I don't get it.