Hi tom. So bravo to you for getting your life on track and making yourself a priority, and frankly also returning here with such a good attitude despite sometimes hearing advice you can't like.
If you'd allow me to put in my penny's worth, here's what I observe.
My experience has taught me that the obly way to judge, predict and understand any of these shenanigans is through looking at the actions that take place, the actions of the narrative and relationship on their own, because they always tell the story truthfully in a way words just absolutely don't. I promise you this.
Here is my opinion of the actions. He had an affair. He half-heartedly ended and resumed it many times. He lied about it and you discovered it. After this he left the family home (prompted by you if I remember). He then made contact again with the OW (probably never really ended totally) and explored the possibility of a relationship with her, maybe seeing her and sleeping with her, depends on the practicalities. She eventually rejected the prospect of a long-term relationship with him. He hid all of this from you, lied about it and then decided rather than having nothing, he would say those things that would encourage you to take him back. You will take him back and you will commit to making an effort to keep yourself the sort of person you want to be.
You may think some of the above is supposition but I really believe that's what's happened and it fits all the facts way more than anything else. I think that's the story. You need to decide whether that is satisfactory for you.
Whatever you say, the signs for you taking him back have always been there. I'm a stranger on the internet and I was sure you would take him back, even when your words said otherwise. Principally because you have always maintained a line between the 'he' who had the affair and the 'he' you married and talked as if you had to work out which was 'real', Which is a completely understandable but ultimately self-protecting way of looking at things. It allows you to convince yourself that you can split him and then only be in a relationship with the latter, purer version of him when the time comes. When in fact, of course everyone is a sum of ALL their actions and one must integrate them into the whole man and then accept you are in a relationship with him to truly move forward.
If I could see that inevitability, I'm pretty sure your DH who knows you well could too.
I'm not saying you should 'leave the bastard'. I don't have a view on it. I'm just telling you what I perceive to be true.
In your latest posts you have committed to all the changes YOU will make to ensure that the relationship lasts. I am afraid that still places all the onus on you to 'make it work' where realistically almost all of it should be on him. Just changing what YOU will or won't put up with is not enough to make a relationship work, since it's relatively easy to hide behaviour from another.
It may well turn into an extension of what things were like before, put simply, you are making yourself responsible for his fidelity even though you are framing it in terms of personal development. I wonder what you would feel if you were to find out he had been unfaithful before in your marriage, multiple times. It is unlikely you will ever find out, since he has not even had the self-awareness and humility to be honest with you about his phone recently. But it is fairly likely that happened, since the vast majority of infidelity is never discovered and you came across his recent affair by chance, not confession.
I'm not saying he will necessarily cheat on you again, what he will have learnt from this is that he must say certain things to get what he wants. So he probably will. His actions go largely unchallenged.
I genuinely wish you the best of luck. It is my opinion that were you to genuinely detach and find a life without him first, and to accept that he is one man, with all the traits that have been exposed here and still decide you can make it work with him, and then if he were to be completely honest with you about what has happened, particularly with the OW recently and take the risk of your anger and loss, to show how different he is going to be moving forward, you would be on the first small step to making a new relationship from the wreckage. Without those beginnings, I fear we will see you back here as we have seen so many others in a couple of years, regretting brushing things under the carpet and calling it 'not sniping'. I truly hope not. All the best. Blood.