One of the thorniest and most difficult things we humans are ever called upon to do is to respond to evil with kindness, and to forgive the unforgivable. We love to read stories about people who have responded to hatred with love, but when that very thing is demanded of us personally, our default seems to be anger, angst, depression, righteousness, hatred, etc. Yet study after study shows that one of the keys to longevity and good health is to develop a habit of gratitude and let go of past hurts.
Want to live a long, happy life? Forgive the unforgivable. It really is the kindest thing you can do for yourself. Your enemy may not deserve to be forgiven for all the pain and sadness and suffering purposefully inflicted on your life, but you deserve to be free of this evil. As Ann Landers often said, "hate is like an acid. It destroys the vessel in which it is stored."
In other words it takes more energy to hate a person then it does to forgive and let go so you can move on with your life. Most people will either mull over or fester in the pain and roll in over and over again for years when they don't realize that it is a lot of wasted energy.