Oh, probably with "Have a nice day."
This is a heartache for me, though it is actually my daughter's problem. She is married to a womanizing louse who takes no particular pains to cover his tracks. They have been married for 11 years, and "the trouble" was apparent soon after they married. My daughter is torn about whether to cut the creep loose or to hope against hope that he will change. There are children. You are experienced, and I am assuming you have a thought-out opinion on this type of situation. Thank you.
Prudie agrees with the late and witty Mo Udall, who said, in another context, "That condition can be cured only with embalming fluid." Prudie also thinks guys like this are lucky if they're not Bobbittized.
It is likely that you and your daughter have discussed this, but the next time it comes up you might point out that tomcat habits are not likely to change and, further, that children are not benefited by having tense and angry parents. Additionally, through some kind of family osmosis, children pick up that a parent is a philanderer, and this, in turn, gives an unspoken OK to such behavior. The decision must be hers.
As a mother herself, Prudie hopes you can disengage on a gut level from your daughter's difficult situation and that you can achieve some peace of mind knowing that adults get to make their own decisions about their lives. Be a shoulder for your daughter, and let's hope she decides the best course for herself and the children.