WHAT IS FORGIVENESS?

What is it, and why is it so important?
First, lets look at something. We all learn lessons from each other.
This is a big part of why were here in the first place. When someone does something to wrong you, the bad feelings you have about it affect you.
They preoccupy you and affect your own experience of being you and living your life. If you stay in the hurt and anger you feel, you will carry these feelings around with you. They will become a part of you.

Other people you interact with will feel them in you. They won't enjoy it any more than you do.
THE OLYMPICS OF EMOTIONAL HEALTH

The olympics of emotional health is to find the lesson in what was done to you and use that lesson to grow and become the new you, then privately (within yourself, unless you feel like verbally thanking them) thank the person who wronged you for the experience.

Yes, that is the healthiest way to experience a wrong doing. Yes, it can be done! Yes, it takes emotional work to do this!
It takes the desire to make the growth you get from the experience of being wronged (and the new you that you get to be), more important to you then the wrong that was done to you.
WHO IS IN CHARGE?

Or, you can carry around the hurt and anger. Let the experience change you for the better. The person who wronged you was in charge of what they did. You are in charge of what you do with it.
Notice I didn't say "what you do about it". I said "what you do with it". By doing something "with" it, you are acknowledging there is a lesson to be learned from the wrong doing, and you are acting in cooperation with finding and learning that lesson.
EMOTIONAL FREEDOM

"Acting in cooperation with that lesson" means looking beyond the person who did it and what they did, to find the lesson. When you find it, you incorporate the information you get into who you are, how you think and what you do with your attention and energy.
Being angry and holding onto it is acting in resistance to that lesson. This is an act of giving up your power, because you're not allowing yourself to find the lesson and become that new person.
Learning the lesson contained within the wrong doing and using that experience to grow is spiritually and emotionally powerful. Simply put, it creates more emotional freedom for you.
It takes courage and self esteem to focus your attention beyond what the person did to you. Looking beyond the person who "did it" allows you to look for the lesson. The lesson is always there.
WHAT IF THE PERSON WHO DID THE HURTFUL THING IS YOUR SPOUSE?

Then your spouse has to change that something in them that caused them to do it. They have to be willing to find it and change it - and become a new person as a result. This change needs to happen within conversation with you.