You went astray and cheated on your spouse. You now regret your actions, but how do you say sorry for cheating? There are no words that you can use to justify your cheating or make it right. You will always be responsible for your actions. However, there are some things you can say that will show your partner that you have truly repented of your betrayal. What you say can even help you to restore the lost trust so that you can save your relationship.
You will not do anything that will suddenly wipe away the pain that your betrayal will have brought to your partner. Although there is no way in which you can excuse the mistake, you should be aware that you can use this as a stepping stone towards a more stable relationship.