Help me! Boy is being flirted on by younger girls! How do I deal without looking like a b---- ?!

I need some major help. Quick!
I'm a senior high school girl who's having a love-hate relationship with the guy I've know since 6th grade. We were best friends all through junior high, but when high school came around, he started to try to get me to go out with him. I went out with him for a week in 9th grade, thinking I'd at least TRY....then after a week, I broke up with him. He was too much of a mushy romantic for me.
Well, then he kept trying. And trying. And TRYING. He'd talk bad about my boyfriends, flirt with me right in front of them (though flirting with us is always an arguement and a few pervy jokes), and say I was "his girl" and that he'd "beat the guy's face in if he hurt me". Yes, he's stubborn and crazy like that. And yes, it is kind of cute.
Anyways, you can see how adamant he was at trying to get me to go out with him, even when I acted bad-tempered to him, talked about boys in front of him, and tried every which way to get him to just be my friend. Yet, you see, the whole plan backfired when my first serious relationship with my childhood friend and first prom date failed this summer- Chris was finally at the brink of giving up on me, and had sent a voicemail in May that stated he didn't want to talk to me for a while. Then in June, my boyfriend and I got rocky together. When Gabe finally said the "I thought, later on, you'd change for me," I finally ended it out of anger and pride- but I was devastated. I had lost my oldest friend, who meant everything to me because he had been my only friend in elementary school when I was the scapegoat for my class and got constantly picked on. I felt like I didn't have anyone in my life that was as close as that to me, who knew me that well, and I was overcome with loneliness.
An hour after the breakup, I mechanically called Chris. He picked up the first time, and instantly heard I was upset, though my pride tried to cover it up. I told him I just wanted him to come over and hang out, but when he came I ended up talking to him for hours and hours, until i suddenly cried on him (something I would never never NEVER do infront of him, for very good reasons!). I'm not a sappy person, and I usually don't let people know how I feel because I feel like I look like I'm starving for attention...but I couldn't stand to keep those feelings bottled up, and I didn't care if the most arrogant, smuggish, most overdramatic guy I knew saw icey me break down like rain.
I sat in his car, curled up and leaning on the window, and cried. Not pretty cry either- I balled with odd sucking noises coming from my head. As the car sat on my driveway, I started to get out as I told him I wasn't feeling good and I'd call him later. Yet he didn't let me leave that car- he made me turn around with his hand on my neck and kissed me. My 'wtf' face kind of blinked at him, but then we kissed some more, talked, and kissed....and I guess after that I became more easy with the idea of going out with him. And this is why a month later, I AM going out with him, and I'm having this problem...
....and now I've just remembered the problem! Sorry everybody for wasting your time with that story- you have no idea how often it is that happens in real life! But I think its a better foundation for my story than if I just told you my problem.
Here it is: When we got back to school and before he and I started dating, Chris got kicked out of one of his classes and switched it to my dance class (whether he was trying to be sweet and finally have a class with me after years of only meeting at lunch, or whether my secret 6 year belief is true, that he IS gay...its unclear...he also went with me to try out for Romeo and Juliet and got Adam as I got Sampson. The funny thing is, we're the opposing servants in the first scene, and we have to fight each other. This works, because I've always had no problem pretend-punching him in the face...ack! Getting off topic again...). There's only one guy in the class, and about 30 other girls. I didn't see the immeadiate danger in this, but its obvious now I should have- Chris is very much a social butterfly, and is very VERY friendly with people, not matter how little time he's known them. Plus, (and this I didn't notice until yesterday) Chris has become a hot piece of meat since middle school...this was unnoticed by me, who still remembers the mexican looking kid who I called "Midget" for so long and who used to get upset that girls ignored him. Now, all of the sudden, I have to deal with flirty 9th grader girls (they make up 80% of that class) trying grab up my senior guy....right in front of me!! And he...he doesn't even think they're flirting. "They're just being nice to me. *grins evilly* Why, are you jealous...?"
Jealous?! I've never been jealous- there's never been a reason to! But I guess there's a first time for everything.
Yes, jealousy is a first for me; I have no idea how to deal with these girls preying on Chris. I shouldn't think of them as predators, since I am 3 years older than them....but the only reason guys like me on a mental level is because I understand GUYS more than GIRLS. So trying to keep my boyfriend with me and keep bitches back with girlish ingenuity and charm...is beyond me. Plus, I'm an easygoing person. An extreme insult to me is to be called a 'b---- ', because its just not true- I never try to steal girls' boyfriends, or talk bad about people, or start any drama at all. I'm just the friend who gives advice about 'what guys think' and watch them dig thier own 7th cirlce of hell with high school drama games.
So what do I do?! How do I get them to back off- do I really have to literally get in thier faces in the locker room and snarl at them to keep off...? I don't want Chris to think I'm being overly possesive, or immature, or...or a b---- ! Plus, does me keeping girls off him make this a serious relationship, which Chris and I know we don't want after both of our last breakups with serious people. How am I suppose to get through this part of my life, without embarassing myself? I want this jealousy to go away so I can move on.