This is one of those actions which benefits you the forgiver and the person you forgive. And all it takes is a choice being made. That you will no longer hold onto the anger, hurt and resentment. It doesn't even have to be for their sake but your own. You are the person eaten up by the negative feelings, creating stress, lowering your immune system and generally making life difficult and shorter.
What is it that I have to do, to forgive, be happier and live longer?
I'm going to try it. Why don't you?
*Whitbourne, S. K. (2013) 'Live Longer By Praciticing Forgeiveness: Forgiveness Can Help You Feel Better and Even Lengthen Your Life', Psychology Today