Are you aware of the joy-stealing effect an unforgiving spirit is having on your life?
Start by telling God how much it hurts and that you need Him to help you forgive the offense. Get rid of all the poison of built-up anger and pour out all the acid of long-term resentment. Fully forgive the offender.
Once that is done, you will discover that you no longer rehearse the ugly scenes in your mind. The revengeful desire to get back and get even will wane, and in its now empty space will come a new spirit of joy.

Walk in a manner worthy of the calling with which you have been called, with all humility and gentleness. (Ephesians 4:1-2)

Bedside Blessings
Charles R. Swindoll