Maybe you could write her a letter about how you are sorry for what you did even though you did not take things further than you did. Yet, show confusion about how you simply don't understand how she could trust a man that is doing much worse to his wife than you ever thought of doing. And you could say, "I love you and care about you and if you decide you don't want to stay married, I have to say that I am concerned for your well being if you were to go any further with this other man that has the capability of hurting you by being deceptive as he is with his wife. Tell her, "I don't understand how you could respect someone who would go that far either".

You could also add in that you are actually proud of her for getting her nursing degree and you do understand that she is just at the point in her life where she wants to be more than just a mommy and a wife and you respect that.