Do NOT report him to the dating service! This will not prevent him from going to another one (in fact, he’s probably registered in several already) plus it will alert him that you know. That is one situation you do NOT want to be in: he knows you know, your daughter doesn’t know, and he might be extremely determined that she never finds out = the physical/psychological issues that you are experiencing now are nothing compared to what you’ll experience at that time and compared to what he might do to you, especially if he’s controlling! Of course, if he’s a master of manipulation, he will pride himself in being able to manipulate his way out of it – but I don’t think I would take the chance that he won’t react in a physically revengeful, controlling way.
If your grandchild is NOT due in the next week, you should sit your daughter down immediately and discuss it with her (I have given a suggested way of revealing it to her below) since this is extremely hard on you physically and psychologically. The longer you wait to speak with your daughter, the more physical damage you are doing to your body. Soon you will have ulcers and other digestive issues along with affecting your immune system. That is why you should address this issue with your daughter as soon as possible. Also, whether you do it before or after your grandchild is born, it has to be done. Your daughter’s husband will be found out (whether one of your daughter’s friends discovers his picture on a dating website, he is seen out on a date with someone, one of the girls he’s dating mentions his name to a common acquaintance of your daughter’s, etc.) and it would be a total destruction of trust for her to find that her mother knew but didn’t tell her.
If your grandchild is due within the next week, I would wait till after the baby is born. The emotional state of the mother does affect the baby while the baby is in the womb (high adrenaline levels, etc.). But whether the baby is out of the womb or in the womb, the baby will still hear, feel and sense the parents’ tension and heated discussions. In fact, I would print this response out and keep it along with writing your own thoughts and expressions of love toward your daughter stating how much your heart hurts for her and how much you wanted to tell her - if you decide to wait. That way if she finds out during the week that you are waiting for your grandchild to be born, you can give it to her – even if she doesn’t know you knew. You have to be honest and ask her to turn the tables - what she would she do?
How to discuss it with your daughter: Have her come over to your house and when you sit down with her, have the printout of the screen in your pocket, in a folder - somewhere she cannot see it yet. Before showing it to her, hug her, sincerely (with emotion and with true, deep meaning) tell her how much you love her and will ALWAYS be there for her – do not skimp on this part, spend a lot of time and emotion – let her know you mean it with all your heart! In fact, imagine that this is the last time you will see her and you want to tell her all the things you will never get to tell her again. It is extremely important that she knows that even though her world might be turned upside down, she has someone solidly there for her. If you do this correctly, she might even ask you if there’s something you haven’t told her – have the doctors said something to you that you’re not telling her. You tell her, “no, I just need you to know that I love you so deeply and that I’m here for you and that’s why I have to tell you this.” Then show her the screen printout. If you have decided to wait till after your grandchild is born, arrange with your daughter for you to watch your grandchild while they meet and discuss her husband’s indiscretions.
Tidbit of advice: If your daughter’s husband has never taken his profile off the website or informed her that he had previously been married BEFORE they were married, he is most likely hiding much more. Also, since he has a controlling personality then it is a strong possibility that he will act out physically when she discusses it with him. I would suggest that your husband be present. Be sure to keep the copy of the screen printout and make another copy for her so that she can pull the profile up on the computer in front of her husband when she discusses it with him. If you give her your only copy, he might destroy it and if, in the future, a divorce is imminent, you have proof that he was at least in the market for indiscretion. I strongly advise: your daughter hire a private investigator and get proof of indiscretion before addressing the issue with her husband. I would also suggest that she find another job, beyond the reach of her husband.