My daughter is 27 and dating a married man with 5 kids, he is 37. He is highly highly intelligent. My daughter has lots of life experiences and says it is ok, that she is in charge. He says he will leave his wife because he feels really loved now. He said he did all the things his parents expected of him. He is a really high achiever and in the Air force. He says his wife won't discuss their problems and says after his posting he will leave his wife, divorce her and marry my daughter. In your experience will he. What should she do. I am worried about her.
I understand your worry about your daughter, but it is her life. That being said, it might be useful to let her know of your concerns, without trying to pressure her into following your advice.
My suggestion would be that she not stay involved with him, and certainly not make any serious commitment (e.g. move in together, etc.) until he has clearly left his wife, and started divorce proceedings. It seems that many times men in unhappy marriages have affairs, promise their paramour they will leave, then change their minds and go back home.
If she continues dating him before he leaves his wife, and his children discover this, they will always resent her and see her as the one who broke up their parents' marriage.