They say that the opposite of love is not hate, but indifference, so your hatred toward the one you used to love is actually a reflection of the strong love you used to feel -- and possibly still feel. Channel your emotions into positive thoughts of compassion and forgiveness, and you'll find that your feelings will once again turn to love, although it will be a much more detached type of affection.

Your Thoughts Are a Choice

Sometimes it can feel as though thoughts have taken over your brain and made it impossible to think of anything else other than how your ex-girlfriend lied to you about her feelings for your best friend. This is not the case, however. Once you become aware of your thoughts, you can turn your mental dial to more uplifting thoughts. Grab a good book, sing an upbeat song, or call a good friend and ask him if he wants to get together and jam in your garage. Keep on top of your thinking, and eventually, you'll train your brain not to go down that dark path.

Forgive The Person

Forgiveness is "a decision to let go of resentment and thoughts of revenge," says the Mayo Clinic website. You can choose to forgive the person you used to love, no matter how heinous his actions. Don't confuse forgiveness with excusing his behavior. You need never associate with him again, if you wish, but letting go of your anger toward him will increase your overall well-being. Psychologically, you will move away from the role of victim and be able to take greater control over your life.

Cultivate Compassion

Kindness and compassion help us to better cope with suffering, says compassion-focused psychologist Dennis Tirch in the "Psychology Today" article "Closer to Compassion Part One: Why Do We Need Compassion?" Cultivating this sensitivity to the suffering of others can help you to see your ex in a new light. For example, he may never have had a model of a healthy relationship, leading him to make choices that hurt you. When you realize that he is in the same boat of suffering as everyone else on the planet, you'll be free to let go of your hatred.

Wish That Person Well

In the gospel of Matthew, Jesus advises his followers to "... love your enemies and pray for those who persecute you." You don't have to be religious to reap the benefits of this counsel. Spend some time each day hoping that the person you used to love will be blessed with every blessing that you'd like for yourself. If you don't pray, meditate or think on this. Your attitude toward the person will be transformed, and you will be set free from the hate that is twisting your stomach into knots.