I don't think it's wrong to ask him to stay, so much as it would be if you pressured him to stay. Saying, "I'm committed to our marriage and I'd like you to stay here with your family while you think about what to do next," is fine. Begging, pleading, getting angry and/or talking about M and R all the time would be a mistake. You want him to feel comfortable staying and being at home, and not like it's a ploy or a trap or just plain miserable.
Now, that said, to keep the pressure off you have to allow him the option to leave if he wants, and do not be surprised if he takes that option. In fact, don't freak out if he announces such a thing. If he is really undecided, then the ambivalence is probably killing him. If he has a conscience at all, having OW is probably killing him too. He may be getting pressure from OW on the other side and while you may have more staying power than her in the long run, she may have a little more pull while he's in the fog. If he decides to leave, be straight about how you don't want him to go, but that you won't stop him. (Truth is, you can't stop him if he wants to go, and trying will only make both of you miserable and/or mad.)
The best way to be ready to handle the possibility that he might leave is the same way you can attract him back. Keep working on yourself for your own sake and go about getting a life. Try not to let yourself get sucked into agonizing over your situation, but rather focus on your kids, your friends, your hobbies, etc.
