should I tell this married man's wife he slept with me while she was 9 months pregnant?

[j s]

This happened about a month ago. I knew he was married, and I am ashamed at myself for what I did. But I did not know his wife was 9 months pregnant. He was with me the night before the baby was born, and I found out the baby was born via facebook. He is an ex-boyfriend of mine. He has posts on facebook telling his friends how amazing and incredible his wife is, yet he has been trying to get me to hook up with him for months, and finally suceeded. I have long lists of facebook and text exchanges of all his dirty talk and professions of love and lust for me. I feel so terrible. Should I tell his wife or just let it go?
just want to add I recognize what I did was very wrong. But what he did was worse. I am not interested in ruining anyone's life. Just trying to put myself in his wife's shoes and if I were here, would I want to know?