You sound like the male version of me in many ways.
I would start with this, if you haven't done it already....it went a long long with my H when I said it, and I was as serious as a heart attack: (Not exact verbage, but you'll get the point) "H, for a while I've been wanting to say this to you because you deserve to hear it and you deserve me to say it sincerely. I have been thinking about my part that got us to where we are today. (And that would be separated at the time, with him deep in an EA that at the time I didn't realize was a PA for a short time) I want you to know that I'm sorry for the short fuse. I am sorry for the blow ups that really were exaggerated. I'm sorry for the many days, weeks and months you felt you were living on eggshells. I am sorry for putting so much before you and taking you for granted, assuming you would always be there. I'm sorry I over estimated my worth. Basically I'm sorry for my part in getting us here."
It was much longer than that....but I think you understand. I made a list of everything I had done to be a crappy wife and spouse. I had our S and changed careers about the same time. I had a friend getting divorced (ironic huh?). I started to exercise more and took up tennis, sort of half a$$ed, but I did. H was definitely put behind all of that, maybe not the exercise and tennis, but he was not the priority in my life for way too long. I changed our sex life....meaning, I slowed it down a LOT and I made it pretty boring. I stopped going out almost 100% and when I did, I went out for about an hour or two and wanted to go home to the baby. I developed a hair trigger temper. If he said he'd be home at 6:00, so help him if he wasn't. Then he tried to not tell me what time he'd be home from whatever....so help him again. It just got worse and worse.
I could really go on.
And in my defense, he wasn't perfect either, but I can say that as we pushed ourselves toward separation, I was 51% of the problem, he was 49%.
And during our separation, there was the EA/PA...with co-worker OW. I'm working on getting my feelings around all of that now. And H is really starting to help me with that in his own way and also some ways I've told him I need.
Basically, like my H told me....he is scared my changes are all BS. He is waiting to see. He was completely honest about it. He hopes they are real and sincere and will last because he does like them, but he's leary.
On my end, I've told him I will NEVER do this again. No more EAs, and really really, no more PAs.