My Dear
I want to believe that you have performed your God-given duties as a mother by bringing up your daughter with the right set of values. I sincerely hope your daughter did not learn that it’s ok to get involved with a married man from you. You may not know this, but, children are influenced by the actions of their parents more than their words. In most cases, the young ones just copy what they see.
I would advise you to call your daughter privately and let her know that she is bringing the family name to disrepute and that her action is giving you a lot of concern and making you very unhappy. Make her understand that you repose a lot of confidence in her and there are certain things you don’t expect her to engage in.
Talk to her with genuine affection and explain to her that the much older man that she’s dating is just using her as a side piece and there’s no future in the relationship. Whatever material gain is attached to their relationship is not worth the price of tainting her reputation or obstructing the love life she’ll have in future.
Also, make her realize that she’s putting herself in harm’s way of being attacked by his scorned wife whose aim is to protect her marriage.
Most daughters love their mothers and hold what they say in high regard. (I hope this is true in your case.) This being the case, I will expect your daughter to appreciate your honestly and take the necessary steps needed to end the relationship that will only end in pain.
Encourage your daughter to date people in her age group, which is far healthier for her mental and emotional well-being. I am sure she will understand your position and make good on your advice. Be patient with her and act wisely.