Forgiving someone who has really hurt us is one of the most difficult things to achieve. One of the reasons it is so challenging is because we believe that the guilty party is simply undeserving of our forgiveness. We don't want to let the perpetrator "get away with it". So rather than forgive, we choose to carry feelings of resentment and anger for long periods of time.
Forgiving is made more difficult by a common misunderstanding of its purpose. Forgiveness is not a gift or a dispensation that we give to a person who has wronged us. It is a gift that we give to ourselves. Its purpose is not to proclaim the other party's innocence, but to rid ourselves of negativity and resentment. Walking around with intense feelings of anger and antagonism is bad for our self development. Hate, pain and animosity cause dysfunction and hinder our progress as human beings. Happiness, hope, a positive perspective and optimism are crucial for our emotional wellbeing and spiritual growth.
There is a prayer of forgiveness that some people recite every night before going to sleep. It begins by saying: "Master of the universe I herby forgive anyone who has angered or wronged me." The interesting aspect of this prayer is that it is said privately. The person that is being forgiven is totally unaware that this is happening. Forgiveness is about the forgiver purging his/her soul of traces of hate and feelings of revenge. While it is important that eventually the recipient does become aware, it is not crucial to the process of forgiveness.
When we forgive we don't have to condone evil or become passive recipients of abuse, slander or pain. But we can still find it within ourselves to forgive and free ourselves from the clutches of negative emotions. So if you have had a fallout with someone, give yourself a gift - forgive and move on.