Can not blame yourself for the actions of another. Say, another person is a thief. You are not that person. He may have stolen from you but you are not to blame for the theft. So, this person came back into your life and you fell for him. Only to learn the truth later. You are not to blame. But, you should learn that your actions carry weight, consequences. After this, talking or writing will release some of the tension from this situation. Later, you must let it go and not bring it back to mind. Stay in the present moment and the thoughts will occur less. The memory will fade. (of course, easier said than done).

What comes to mind is a scene from a movie. The man cheated on his wife. He says to his wife that the affair with the other woman did not mean a thing to him. The wife replies, you threw away our relationship for something that meant nothing to you. Which means that their relationship is equivalent to the affair he had, meant nothing. If you value something then do not throw it away for something else that means nothing. Well, enough from me. Wish you happiness.