Write a letter to the person (or people) you have been harboring resentment toward. Explain exactly why. Tell them you have forgiven them entirely.
Then, DESTROY the letter - DON'T SEND IT.
*Share your experience on Comments.
"But I tell you, love your enemies and pray for those who persecute you, 45 that you may be children of your Father in heaven. He causes his sun to rise on the evil and the good, and sends rain on the righteous and the unrighteous. 46 If you love those who love you, what reward will you get? Are not even the tax collectors doing that? 47 And if you greet only your own people, what are you doing more than others? Do not even pagans do that?" (Matthew 5:44-47)