In love but insecure, need help!?

im 19 and dated this girl for about a year. we were crazy in love with each other, until i found out that just before things started to really kick off she had slept with one of my friends. i found out a few months into us dating and it shattered me, never really got over it. she is 2 years younger than me and has a promiscuous past, but as a girlfriend she was awesome and did everything for me. perfect match, i just never really got over the thing with my friend and her past. broken up now but still love her, what do i do?