I am so sorry you are going through this journey. My ex-husband was unfaithful with three women during our marriage and when I found out, I started the divorce process. We were together for 22 years.
Nothing will take the pain away but time. I suggest journaling and write down all the things that brought you happiness as a child before you met him. Do those things with fresh memories. . If you let your soul open to it, you will experience a new beginning that isn’t defined by him. In time, you will be able to say thank you to him for “freeing” you from constraining pain. You were not your best self with him. You now have the chance to be.