Some people are driven by anger and resentment, due to those things happened in their past or provoked by wrong experience. With these they keep the hurts they feel inside and never learn to let go of it. Instead, needing to release it through forgiveness they just continually and repeatedly kept it in their minds.
You know,those persons who hurt you in the past cannot hurt you anymore unless you let them hurt you again or you continue to hold on those pain through resentment :( with the famous saying : "PAST is PAST" you should never allow you past to control your future. We are products of our past but we should not be prisoners of it. If you gonna keep it, then your hurting yourself more with your bitterness! What you need to do is to LEARN and then LET GO OF IT!
Sometimes, through all the resentment and anger you've felt you will realized and find it in your heart to FORGIVE. Forgiving those people who gives you pain, broken your heart, rejected you and didn't see your worth. I know its not easy at first, but freeing yourself from all those pains will give you not just peace of mind but even a healthy and happy heart :)♥eventually, at the end you will just FORGET and laugh at it once you remember it..:) anyways don't worry, God specializes in giving people a fresh start :)
so.. learn to let go and nothing tastes as good as the feeling of being far away from bitterness and pains! so im giving you this advice from my happy heart to your "soon to be happy heart" :)