How can I be more trusting and confident in myself?

Not trying to sound full of it, but I am a pretty attractive person. But, just like anyone else, I have had some pretty bad relationships in the past. Particularly my first "serious" boyfriend back in high school. Plus, I feel like I am not "good" at anything really. I'm considering picking up a new skill for a self esteem boost. Still, I must admit, I don't treat my current boyfriend the way a star girlfriend should. I stopped doing most of the stupid shit, like hanging out with guys(never alone) and having a drink or two(never getting sloppy in anyway). Yes, I would flirt a little. But, I never liked any of them. I only wanted a self esteem boost. This sounds terrible, I know. My boyfriend always tells me he loves me and he is the best ever! I never told him about the lame parties with guys with my chick friends because I don't want him to know just how down I am on myself. I know what I did was wrong, but I feel like I still have a chance to correct things. I mean, I know hanging out with other dudes at a party probably was not right, but I never touched them and they knew I had a boyfriend. How can I trust my boyfriend more? I'm always scared he will find someone prettier or just overall better than me in everywhere possible. He fell in love with the old me-confident, sexy, silly, happy and just overall fun to be around. How do I get the old me back? Please help!