I think forgiving someone is hard for a lot of people. Some people are naturally inclined to forgive others but I'm not one of those (I wasn't gifted that way).
I know I'm instructed to forgive by God's word. If you search the word forgive on www.biblegateway.com there are 116 results so I know it's important if it's mentioned that many times.
Matthew 6:14 For if you forgive men when they sin against you, your heavenly Father will also forgive you. 15 But if you do...