"I think what holds us back from letting go of anger is that we don't forgive as long as we need to blame. And we need to blame as long as we are unable to admit and feel the hurt from being injured by someone else. And we are unable to feel the hurt underneath, because doing so makes us feel vulnerable and fearful of a second attack that we are convinced would be too much to bear."
Easier said than done but it is a start.
[Link to How to Let Go of a Grudge]