Why do I feel sad about myself?

Today I am graduating from community college and I feel happy of my accomplishment.However,I feel that I don't deserve it.Its been 3 years of dreadful years,mainly due the events from high school (mainly senior year).Since I was heartbroken in senior year,this girl has affected me quite a lot.I still haven't been the same since that year.I've worked minimum wage jobs,took remedial classes all the way to hard sciences,and been able to talk to other girls more easily.Yet,she is still in my mind although she lives 1000 miles away.Is there a way I can feel more confident about myself,forget about the past,be myself?