How do I stop caring about what other people think?

I recently messed up really bad. I know I did really wrong and hate myself for it. But it was a while ago and its caused everything in my life to be messed up too. I've lost friends. I no longer am part of a group where I feel included or cared about. The friends I do have I am greatly appreciative for, but I never get the opportunity to hang out with them. I lost the guy I love, we still talk and we still love each other, but he can't take me back until he's back in the country. The worst thing that's getting me down is the way people treat me, like i'm scum of the earth. And I know the only thing I can do is stop thinking and caring about these imbeciles... but how?