Forgiveness doesn't excuse their behavior. Forgiveness prevents their behavior from destroying your heart. Deciding not to forgive hurts not only the other person but you as well. Not learning to forgive hardens the heart and makes shallow the soul.
"The beginning of love is to let the one we love be perfectly themselves, not twist them to fit our own image. Otherwise we love only the reflection of ourselves we find in them." - Thomas Merton, No Man is an Island