I turned 73 last Summer. My W's A was 7 years ago; d-day was just short of 7 years ago. We just celebrated our 50th anniversary.
I think the first thing to start telling yourself is that there can be a good life after being betrayed, whether you stay or go or kick your H out. Believe me, it's very true - you can have a good life.
Your post actually reads like you're on your way to a good life. It won't come fast enough, but it can come to you. Expect some more time going deeper into grief, anger, fear, and shame, then a gradual plateauing for some time, and then a slow climb back up to joy. If you like your grandkids and can be with them, you might feel real joy sooner than that.
As everyone above says, focus on your healing now. You did nothing wrong - your H cheated because of his issues - but lots of feelings have been dumped on you, and you need to process them.
It's hard to think while under the stress of being betrayed, so don't press yourself for quick decisions. You want good ones, and it will be a while before you can know what you want and the best way to get it.
I really hate to say this. I don't mean to be cavalier. But your H brought this stress on himself. He could have not cheated. He could have found some courage and come clean 17 years ago. He didn't. He chose to wait until his health was messed up.
His stress is his problem, not yours. It's very possible that working through this will free him from stress he's been carrying around with him for 17 years. In other words, if you need something from him, ask for it. It may help him as well as you.
I echo the reco to find a good IC to help you process your feelings and figure out where you want to go from here.
You can choose R or D with your head held high. You can move or redo any part of your house with your head held high. You can focus on yourself and keep your head held high. If you're not ready to decide, you can hold your head high. You're at an age when there are more women than men - I suspect you'll get a lot of support no matter what you do.
If you choose D, remember the demographics. You shared a lot of good years. IMO, R is best if both partners are willing to do the work in any case. I think that's doubly so when older, because I like having a partner.
OTOH, I've seen reports of surveys which say that single older women are happier than single M women of the same age, and I've never seen one that says the opposite.
Don't press yourself to decide - again, you want a great solution, not a fast one.
WRT mind movies, I let them run. I couldn't relate well to my W while they were running, but I found them to be a lot shorter and a lot more mundane than I thought. I've been less troubled by mind movies than many people seem to be. That could be my personality, but it could be the fact that I let them run.
To R, you heal you, your H heals himself, and together you build a new M - but the M can be healed only if the individual healing has started.
Was the MC recent? If so, look for another MC. Also, your H could probably use IC to help him deal with the part of his stress associated with guilt and fear of losing you.
He didn;t cheat because of your M. Dealing with M issues are at best an indirect way to heal. OTOH, if you want help establishing boundaries in your M, MC might be able to help.
There's so much to learn ... I'll stop now, because it's impossible to read or write everything.
But this is worth reading again: you can lead a good life, even after being betrayed.