I am no stranger to the brain-shutting-down-during-conflict dilemma. The good news is that, with work on oneself, it IS possible to get past that automatic reaction.
I found the work of Al Turtle to be groundbreaking on why the brain behaves like that. It's not something you initially have any control over, and has to do with the way our 3-partite brains are formed, and, he reiterates, it's a reaction that always makes sense. He has a website, where he explains the reactions of what he calls The Lizard--the reptilian part of the brain. He also explains how couples can work together to make each other's lizards feel safe so that they can get past feeling "threatened, scared, angry" etc. I think you might find a lot of food for thought--and hope--there.
Congratulations on how far you've come. All the improvements you describe are wonderful. I'm delighted you are getting your groove back!!
