How do I gain more self-esteem?

I’m a freshman in college, away from home, and I don’t seem to have very much. I know that there could be much worse things, and I’ve always felt like I wasn’t good enough, so I’m used to it. But, my boyfriend isn’t. He doesn’t understand why I view myself in such a negative, unhealthy way—and I can’t really make him understand. At the same time, rather than make him understand, I’d prefer to just work on the problem. I just find that I constantly compare myself to others, and fear that this will keep me from ever being happy. This lack of self-esteem, security, and confidence is really causing problems with him—as I’ve kind of grown used to myself and dismiss it. Any suggestions?