Check out https://survivinginfidelity.com/topics/558762/honey-they-always-affair-down/. You'll see that your H's ap fits the standard pattern.
Also, I recommend checking out the threads in the Just Found Out ('JFO') forum that have bull's eyes next to them, like 'Before you say Reconcile...'.
To you and everyone else: there's no need to apologize for a post that stays within guidelines. We all read basically what we want to read and respond when we want to respond. Initially, I suspect that a longer post may be better, all other things being equal, because the only way to get specific guidance is to write specifically - without breaking anonymity, for your own safety - and that generally can't be done in 2 sentences.
...I feel I am masking my feelings to keep everything calm.
Gently, that's called 'rug-sweeping', and it pretty much always leaves a BS in pain. To heal - that is, to survive and thrive after being betrayed - you have to address the issues directly. That takes time, but more than that, it takes courage, strength, and energy, all of which you have, even if you think you don't.
From what you wrote, your H is not taking full responsibility for his A. His ap is is subordinate! He needs to recognize that he really fouled up in his choice of ap; it would be hard to do worse. (Lest you think I'm beating your H up unfairly, note that my W chose an even worse ap.)
But more than that, he's been blaming you for his own failures. You say you don't know what he meant when he told you he wanted changes in your M 6 years ago. It would have been better if you had told him you had no idea what he meant and pinned him down. It would have been even better if he had told you directly what changes he wanted. It would have been way better if he had invited you to discuss what you both wanted your M to be.
Instead, he just blamed you. That, to me, is abusive.
So what do you want? Do you want to live with him without him making changes? I hope not.
What changes do you want from him? I'd suggest at a minimum that you require 1) honesty - no more lies, 2) willingness to answer any and every question you have about the A, 3) NC with his ap, up to and including finding a new job if they're still working together, 4) IC for him, because he surely needs help to change from cheater-blame shifter-trickle truther-minimizer to good partner.
And I mean 'require' - if he doesn't agree, you really ought to consider dumping him, because he won't be a good partner if, for example, he reserves the right to lie or to avoid taking responsibility for cheating/lying/not addressing his own issues.
What changes do you want to make in and for yourself? A couple of related suggestions: to find the strength to assert yourself and to stop stifling yourself.
I paint a pretty negative picture of your H. That doesn't mean I think you should dump him. Rather, I hope you look inside to find out what you really want and go for that. If you really do want R, you then need to look at your H to figure out if he'll do the necessary work. If you think he will, R is possible - but if you don't see him doing the work, R will fail.
We can't predict the future, and the future without your H may look pretty scary. Just know that you have strengths you never even imagined you have, and whatever the future brings, you can have faith in yourself to heal from being betrayed.