Can any unfaithful spouses out there help me understand why its so hard for him to give the OW up?
I am not an unfaithful spouse however I can tell you from my research that you are dealing with VERY powerful forces in an A. Your H has not finished growing up and the A is giving him what he erroneously thinks that he needs.
I see that you have a DB coach. Have you read the DR book? If not I would get it and read that book. There are many other books that you can read that will give you more info on your sich. You can start DB'ing but it will be very difficult to control your H, and is not something that I advise.