I agree with charbon here, HH. I've been really impressed by your articulacy and awareness on this thread but I think you're smart, very smart and so you understand the moral horror of what you've done and what's expected of you. You know what's the right answer and what you feel on some level, but not at your base. I think you're trying to answer and frame your feelings in a way to rationalise the situation you've left yourself in. I think you want to want things, rather than actually simply, in your gut, want them.
You might not be ready to be completely and utterly honest with yourself. 'Knowing' your DH is a better man that OM in your head is not the same as 'knowing' emotionally, having learnt it properly through experience and throughout your being.
I think you will get there but I wonder if you posted in order to ask how you could be made to feel something you don't feel, instead of for practical advice.
You are confused because you know that your OM would never have left his wife. You know he cared for you less than your DH and less than you deserve. You know you DH is a good man, who you love. And you know the best thing for your children and your family is you making it work. So with all these things, how come you don't feel perfectly motivated and happy?
It's because it was never about those sorts of things.
You are hungry for something, you have a sad, broken yearning in you, like many of us do. On some level you can't believe your life turned out like this. You're ashamed for feeling that because so many people have worse lives than you and you are so lucky and yada yada yada. But you have it and there you go. For a brief time, that hole got filled and something got reignited and loads of other mismatching metaphors. And because it happened with OM, you associate it with him. falling in love or lust is insanely powerful and the cheapest but most expensive way to feel all that.
Perhaps you need to look at who you were with him, what happened. What's the version of yourself you were running towards, the bit that got lost as wife and mother and colleague? You can have an adventure you know. You can break rules or start again or be creative or look beautiful or be spectacular and move towards a better, more truthful, fuller version of your self that is nothing to do with the OM. That is greater than him. You don't need to do it with for or through a man. What is it really, really, you were searching for or trying to reclaim when you were with him? Wealth? Glamour? Attraction? Fun? Power? They are all available to you. And focusing purely on how you can heal your marriage might actually be taking you away from that thing you need to nurture. If you spend all your time whipping yourself and apologising and mending, but what you were really always searching for, say, was a sense of fun in yourself, then of course you're going to feel like it's not 'working'. But that's not your DH failing, it's you, by not being honest with yourself. You have to repair it, sure, but you also do that by becoming and searching for what you need in your life, with him and outside of him, so you don't just take the easy route of finding it in encounters with some philandering coward. (ps was it you who he texted to say his wife had found his phone after you admitted? that really really is likely to be bollocks, OP. I'd bet she never knew anything and he just wanted to hide from any consequences and keep his marriage unblemished).