REALLY want to sleep with a woman. Dating a man.

First and foremost, I would never cheat on my boyfriend. My situation:

I'm bisexual. I've known this since middle school. However, I'm only mildly attracted to men (Really, I'm not attracted to their bodies as much as their minds, what they can DO in bed, and oddly, their hands). Women on the other hand, as much as I've always DATED them for their minds, physically, when it comes down to what makes me hot, it's their bodies, all the way. It's not something I'm proud of, but I can want a woman in bed that I don't want to hold a conversation with.

I've only ever "been" with one man, and that's my current boyfriend (It's rather hard to find a man with a mind I'm attracted to), and he is an amazing lover. I know that I have limited experience in the subject, so it doesn't sound like a credible statement. On average, however, I can expect 3-4 orgasms when I'm with him, and it's not like I have them easily. We have a healthy, active, and advanced sex life. My point is? It's not like he's not "satisfying" me, because he has literally made me scream, squirt, writhe, and cuss until I'm so exhausted I can't move.

All of that said, I want more. I've been with him for two amazing years. He's my best friend and everything I could ever want mentally, emotionally, and spiritually. But lately, regardless of what I try, I cannot stop fantasizing of women. At first it was small, just thinking of them right before bed or something (and I won't lie, there's a particular girl in mind) and I could control it, stop it if I wanted to, or let it play out in the hopes of getting it over with and moving on. This was about 6 months ago. Now, if she (or anyone with a similar body) moves certain ways or is just around for too long, I cannot seem to stop the images in my head, the tingling in my palm to have her under me... It's bad. It's really really bad. I've started watching lesbian porn to try to get the feelings out or something, but it's not helping, (I don't masturbate, I quit that for him about.. 3-4 months ago. It makes our sex about 100 times better, as well.) it's just turning me on a lot. It's gotten so bad that when he and I are "together" and I'm about to "finish", (I love euphemisms) one of the few fantasies that can push me over the edge is having her under me, ah-hem shall we say, pleasing me? while he pounds me *blushes*. Anyways, that's how bad it's gotten.

I also hate that I REALLY like this girl, she has a great personality, and I know I'm not attracted to her for it, but she is one of my best friends, and an ex-girlfriend that has since decided she's straight. We never slept together, because I think she's right, she IS straight. I mean, we never even kissed, much less undressed or groped. We cuddled. Once. Kinda. xD It's pathetic. Anyways, if she had the slightest idea I thought of her in this way, she'd be horrified, and more than a little disgusted. We're too good of friends and I care too much for her to be okay with the things I'm thinking about her, and I very much want them to stop.

Now, I know the answer should be obvious: "Guys love bisexual girls! Invite another girl into the bedroom!". This will not work for me. My boyfriend has jealousy issues (no one's perfect), and my gay-ness makes him incredibly insecure. For the first year we were dating, he was convinced I was going to leave him for a woman (especially the woman that plays lead role in my fantasies). That makes this whole situation worse, and the guilt is killing me. If he knew, he'd be so heartbroken.

Anyone in a similar situation? Or any way to help? I'm rather desperate.. I really just want it to stop.