I'm such a jealous person

I hate how jealous I get. It's eating me up inside. My boyfriend, Mark, is a really friendly guy, and he talks to everyone. I know he's not doing anything wrong, but when I see him laughing with other girls, I just feel this stab of anger and insecurity. It makes me feel like I'm not good enough, like he'll find someone better. I know it's my problem, and I try to control it, but it's so hard. I don't want to be this person, this insecure, jealous girlfriend. I'm afraid I'm going to push him away with my jealousy. I don't know what to do. I try talking to him about it, but it just makes him feel bad, and then I feel even worse for making him feel bad. I just wish I could be more confident and trust him completely, but it's like there's this little voice in my head constantly whispering doubts.