wellwobbly - you asked what my DH did that was different. In answer, everything.
To start with he opened up to me and talked, properly, shared everything in a way he never had before. We both did. There were so many misconceptions and misunderstandings on both sides. It was tragic really, and ironic that two people who really had married for love had drifted so far apart.
Then he took a good long hard look at himself, as did I. I'm not blameless in this. Our marriage had fallen apart at the seams, and I had played my part in that. We've both become better more considered people not just to each other but in general as a result.
Finally he started to treat me with kindness and respect, to put me first above work, his family his friends. I was initially adamant that I wanted a divorce, and he accepted that, but wouldn't even get a lawyer. He would have given me anything I wanted, made it clear he never wanted me to be financially hard up, that he'd support me for life, that he wanted me to be happy. It was so sad, I had never felt so loved or cared for, but at the same time we were divorcing.
Now... now we are finally happy, and together, and we really do genuinely care for each other. He is deeply ashamed. He knows he can be arrogant, and selfish, but he shocked himself as he never realised he could be an utter bastard. He hasn't expected me to blindly trust him, and does everything he can to help me with that. If he has to travel for work I am invited, if he has to work late he tells me first, and is prepared to just walk out and come home for me. I have the password to his phone (I've never checked it, and never will) and he leaves it on the side when he is at home. He asks me what else he needs to do.
I too have changed, a lot, for the better.
If he hadn't done all of this I wouldn't be here today, I'd have continued with the divorce and moved on with my life. I never hated him or his OW, and I like to think that at some level we could have remained friends.