I'll tell you one thing that exposure accomplishes and it was hit on once before in your Newcomer post. It destroys their secrecy. It really takes the wind out of their sails, but it also pushes them and the A partner closer and faster. It will get uglier before it comes close to getting better.
So again, before you decide to expose, you need to be at a better place. I read more of your thread and really if you keep focusing on YOU and get to the point where you know YOU are the person he was originally attracted to then you will be way ahead. According to your own words, some of the changes have made him notice you so keep that up. You also said some of the things he was attracted to is what is pushing him away. Would all out exposure be a similar behavior of yours that would drive him away faster?
TBH I'm not for the ALL out Exposure, IT IS beneficial for HIM to know you know, but in the end it's going to come down to a choice between you and the OW. Are you at a place where you know what needs she is meeting of his? Have you done your work to fix the part of the marriage where maybe you fell short? If you "expose" and if he came running back would you be at a better place to make your M work? Can you expose to HIM what you know without him "justifying" he's better off with the OW?
It's safe to say that you are NOT open to a 3rd party in your M. That is a very good boundary, but are you STRONG enough to enforce and follow through on this boundary and what it will take to hold that?
Last but not least. YOU are not at fault for HIM having a PA ok? I'm not telling you that you deserved that crap in anyway. Nobody does. However, if you want to WORK on your M and you can forgive him, then I really want you to be prepared for what will be needed anyway.
