Is it normal to get jealous so easy?

Is it normal to get jealous so easy? I mean, my boyfriend said some girl on tv had a nice belly and I bitched about it for a whole month, even cut myself over it. Whenever there's a girl on tv who's showing even a little bit of skin or being flirtatious, it pisses me off way more than it should, and I can't stand it. I know he could care less, and I know even when he does say something, it's not like he gets a boner or anything. Nonetheless, he always tells me that I'm the most beautiful girl in the world, and he always calls me sexy/beautiful/or whatever. I'll get jealous over girls he thinks are ugly, even. Or there would be someone who I think is really pretty myself, and I just want to kill her, even after my boyfriend laughs and tells me how much more attractive I am. He's never cheated on me before, and he's honestly the best partner I've ever had. I've had others cheat on me in the past, but I never cared because I cheated on them too... I used to be pretty promiscuous, which is something my love really helped me through. Luckily, when he found out how I was, he was angry, but more so heartbroken, and he helped me become loyal. I mean, my love for him helped a bunch too, but I kinda had issues that I hadn't really told anyone else about at the time. So... I know that's kind of unrelated, but maybe I fear that he's going to go somewhere else because I used to go somewhere else to practically everyone I've ever been with? I just wanna know how to get jealous less often... But, is it normal to be that jealous? Does anyone think my own problems from before I began to heal may factor to this issue?