How to be happy again?

In October, my best friend sent me an email saying she thought i was mean. I felt terrible and would feel like a failure as a person and as a friend. We resolved our friendship problem (there is still not a day i don't think about her) but I still feel like a failure, now just about everything: drawing, singing, grades, athletics, etc etc etc. I feel bad, then i cry, then I beat myself up for being a wimp, then i get mad, then sad, then cry and it keeps going and going. I feel ugly and fat too. I just want to feel happy again... and not feel like i'm going to burst in tears after everything I fail.