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

[Missy]

It both your fault and his fault. No one has 'more' to blame. You are just as much to blame regardless of how much he wooed you. His outcome, however is probably worse because he is married and in hindsight he has more to loose. I don't think by telling his wife you are ruining anyone's life. You are bringing light to something that happened. Now I don't know if you are considering telling his wife to relieve your guilt or because you truly feel that she deserves to know. Either way none of those are good things because all of the sudden you developed this sympathy towards AFTER you slept with her husband.
As a wife, I would like to know if my husband cheated on me. Some people say that she will find out sooner or later and that's just not true. I have known people that have hidden their infidelity for over 26 years! If has cheated once he is more likely to do it again unless his wife pulls some reins. That being said I would tell his wife. Maybe anonymous tip, letter? Give her what she needs and she will find out. If you don't want to get stuck in the cross fire maybe you shouldn't tell her it was you that slept with him. Depending on the type of man that he is there might be some retaliation from him and even the wife.