My suggestion. Don't tell him you don't want a D. Don't tell him ANYTHING! No relationship talk. Let him do all the talking and you listen. If he talks relationship change the subject. Ask how his apartment (or wherever he's living) is? Does he need anything from the house? What fun things has he been doing lately? Nothing personal whatsoever. NO RELATIONSHIP TALK. Now is the time to become his friend. You have to change the "bad memories" he has created. Only light, happy, positive impersonal stuff.
And focus on you. This may or may not work. He may still end this marriage. But you will go down knowing you did your best to save whatever you could. And you will have no regrets. One can doesn't regret trying, it's the not trying that people regret.
There is no arriving, ever. It is all a continual becoming.
