Forgiveness is a gift that you give yourself. Don't think of it as letting the offender off the hook, think of it as you moving on. Why tie up your thoughts and emotions with things from the past? Let it go.
You have better things to do; you have better things to think about. You are thinking about your future. Forgiveness clears your mind - it is a gift that you give to yourself - not the offender. This is not to say that you forget what happened, but that you don't let it bother you anymore.
Time is precious. How much longer do you intend to think about it --- or can you now begin to guide your thoughts toward the positive? Toward the future? Your next vacation? A pet? A child? Anything else. It is your life - live it. Forgiveness is fundamental in a balanced life.