First of all I need to tell you that only you can determine when you have reached the limit as to what you can take and what you can't. You will know when the time is right for you to tell your H...IT'S EITHER HER OR ME!! It just sounds to me like he has some unresolved issues with this OW. I heard Dr. Phil speak once time and he said if a H is willing to give up the physical R with OW but contimues to stay in touch with her then he still has feelings or things he needs to resolve with her. I feel that is the way it was with my H. He had to know that he was doing wrong by staying in contact with her because he has not only broken his promise to me but lied to me about it. He was trying to keep me from knowing about the contact so he had to know he was doing something wrong. But later when we talked he admitted that he needed some "closure" and he told her that he was happy now and that things were going very well with us. He then told her that that couldn't be friends and that she should get on with her life and never contact him again. I tried to understand he needed "closure" and I have let it drop now and have no reason to believe he has contacted her since.
You don't need me or anyone else telling you that your H is being "emotionally unfaithful" to you. Maybe he has stopped seeing the OW (and I sincerely hope he is being honest about that) but that still doesn't make it right that he is in touch with her. You are right when you say he can't be giving 100% to your M if there is someone else in the picture in any way!!
Maybe he is just trying to see just how much you will accept. He has to know he isn't being fair to you or to your R but as long as you are accepting the fact that she is in his life,he will continue to do what he wants. I understand that if you issue the ultimatum you run the risk of him walking out and going to her. But he is evidently attached to this OW in some way so he could possibly go to her anyway. I am not trying to hurt you by saying this but I think you know what the possibilities are. But it could also go the other way. Maybe he is waiting for you to get in his face and tell him he HAS to give her up or lose you. Maybe he wants you to show him just how much you do love him by insisting he get her out of his life or risk losing you. That sounds crazy but there are men (and women) who honestly feel that way. But I don't know your H and you would be the one to know if he is that type.
Bottom line is YOU are the only one who can decide when "enough is enough". Some people can handle more than others. I know I couldn't live like that. I would have to tell him "she goes or I go". I basically did that and I was fortunate in that my H understood my feelings and honered them and knew he loved me,not her and he chose to get her out of the picture and put 100% into US.
Pat