This happens here, too and I feel your pain. Part of me died when "our" marriage ended, for I was the proverbial SAHM and felt alive when he and our daughter came home. I had a life too, but it was small and quiet and I think got too boring for him.
I'm working on a hard 180 as you are and suffering withdrawal, but am proud of myself when I can do it longer and longer. Now, when I don't answer, he will ask, "Is your phone broken again?" Sometimes I make excuses because it's easier and it's an old cell phone so does go in and out of battery use more often.
Anyway, what I've heard from several counselors and even my lawyer is that this is how our WH's live with themselves after what they've done. And Nearly Exh here has put very heavy blame on me, blaming me for every problem he ever had in his life. Well, he's still having some pretty big problems and I'm hundreds of miles away and silent!
Yes, I get your drift of the "shell of a person" and have also heard it called a "pod person". I think of Nearly Exh like that, in kind of an alien, outer space sort of way.
I'm sorry for your hurt-and everyone's here-and I believe that he does understand but doesn't want to deal with it.
A person is a person, no matter how small. -Dr. Suess
Perserverance and spirit have done wonders in all ages.