Do not listen to your feelings which tell you that you will be bitter until the day you die. Call on the Lord to deliver you and give you the strength and power to forgive. You can pray Romans 5:5. Look up the testimony of Corrie ten Boom who survived concentration camp in Nazi Germany and who prayed this very verse when the Nazi SS officer who had cruelly beaten her sister who died in the concentration camp came up to her after the war (Corrie was preaching on forgiveness at a church). The former SS guard told her that he had given his life to the Lord and received his forgiveness and asked hers too. She could not forgive him, she felt only hatred remembering his cruelty. But then she silently prayed Romans 5:5 and the Lord changed her heart that moment and she could shake the guy's hand and forgive him from her heart.