I have not read all of your threads, but many of them. I was in a similar situation, for not nearly as long a period of suffering, and caught some lucky breaks. In my situation, there was an EF involved I was unaware of, and my W was acting like yours.
Since you are "laying down the law" WRT no 3rd parties, there is no way your W is going to tell you if there is someone else, and will certainly go the extra mile to hide it. If there is an OM, you are going to be frustrated in your efforts until that ends. You might consider backing off your mandate here and see what you learn.
My W told me that she was unhappy in our relationship, and that she was seeing an IC to work through it. I considered that a wake up call, offered to do MC (W refused), and then tried doing everything I could to 180, GAL, etc., but all my efforts were getting me nowhere, she was cutoff and detached, and my efforts only seemed to frustrate her and further push her away. I felt like I was with a stranger, and one who didn't like me too much.
I spent many sleepless nights wondering "how can I try so hard and she try so little?" She would make occasional token efforts, and at times seemed to relax a bit and smile, and that encouraged me to keep going, but I could never make any real progress.
Then the truth was revealed, she had been engaged in a fairly long EF with an OM who was also unhappy with his W. They started off as friends discussing their marital woes, and it evolved into an inappropriate EF. One lucky break I caught is that he cut it off and ended all contact to save his M, but when I discovered the situation and confronted W, I was asked for D.
I tried to start fresh, and only after OM was gone, after some period of grieving, did my W come back to the table and even start to consider working with me. It suddenly became clear that all my prior efforts were useless, as it was only deepening her pain, conflicted emotions, and resentment.
If at one point your M was very good and your W was engaged, and now you can get no engagement from her at all, I would be very suspicious that the R energy is being invested elsewhere, even if it's only "friendly" at this point. You will never force the truth out, but it may make you feel better about your frustrated efforts if you realize this is going on, and you can approach the situation differently.
When this happened, I felt horrible, I never knew I could hurt so badly. I am reading the same feelings in your posts, and I feel for you, it's the worst thing you can go through.
Hang in there -- my R is on the path to recovery, still hard every day. Great highs punctuated by terrible lows, but as others have said, you want to look back and remember that you left nothing on the table, that you used everything you had to try to save the M, and even a little bit you didn't know you had.
Best wishes, do it for you.
Married 18, Together 20, Now Divorced M: 48, W: 50, D: 18, S: 16, D: 12 Bomb Dropped (EA, D): 7/13/11 Start Reconcile: 8/15/11 Bomb Dropped (EA, D): 5/1/2014 (Divorced) In a New Relationship: 3/2015