Overcoming Fear and Guilt

I just broke up with my girlfriend of 5 years. Our relationship was far from perfect, it had a lot of problems that seemed to be irresolvable (thus the breakup). However that does not change all the good times. I'm not losing just a girlfriend but a best friend as well. Two of the biggest problems are a fear that I will look back on it I'm the future and regret my decision, and this unbearable guilt that I'm giving up on/abandoning someone that never gave up on me. Its consuming me. I'm wondering if anyone else feels this way and what you do to help conquer it?