Arabella, this is where I was, with the same crappy so-called relationship and a man who took every attempt by me to bring up things that made me unhappy as a personal insult to him, got angry, accused me of a shopping list of flaws and faults, and finally made me feel as if I was being destroyed.
I tried the discussions. I tried the letters. I begged him to come to counselling. I tried basically to clap with one hand, because he wasn't interested. The slightest peep out of me set him off. He made it clear that he did not welcome my input, my thoughts, my feelings. He was and is an angry, miserable, blaming, walking, talking, inadequate little ball of self pity and hostility.
I disassociated my 'self' a lot -- yes I know what you mean here, not actively negative, but I grew a second skin of numbness so that it was possible to get through the weeks, deal with the children and try to he a half way decent mum.
Make your preparations and prepare yourself to separate. I think you are very right to be unsure what else there is inside him besides what you are experiencing day to day, week to week. It gets to be very soul destroying. You don't talk because deep down you know he will probably take it the wrong way and turn it all back on you.