It is not your job to figure out what his childhood trauma may have been. It could very well have been comparison between two children, i.e., your h not being as intelligent as a sibling, or he could have been bullied, i.e., there are any number of things that may have been a "trauma" which would have stunted his emotional growth. He is the only one that can face those traumas and work through them and accept that he was not at fault for what happened. Unfortunately, even if you knew, you couldn't fix his problems because you weren't at fault for them.
When you say sit quietly and the answers will come...the answers will come when they are good and ready. He may open up and provide info that will help you connect the dots. Many of them will eventually start talking and when they do, you will need to really listen, not offer up advice..,.just listen. Later, that conversation will play over in your mind and you will discover some tidbits that will help you better understand where he's coming from in his crisis. Trust me, when you sit quietly, the answers will be revealed, might not be today...but tomorrow or the next. When we drop the rope, focus on ourselves we will learn more that way. Fighting the urge to fix things and just allow things to flow naturally and turning your h over to God to drive the bus and not taking that wheel back each and every day will help not to prolong his crisis. One thing that I learned early on...you can't force the answers to come to you...they will reveal themselves when you least expect them to.
The homework is to work on yourself, detach more, just listen and validate, dig deeper for patience and the most important thing...keep the focus on you. You can't fix him...you didn't break him. This is his journey of self discovery and you have your own journey to travel, i.e., to rediscover you! It is an opportunity to work on you, the list of things that you've put off doing, and to think about the person you were years ago...do you want to be that person again? If so, this is the time to think about any changes that you need to make for yourself, not to convince him to stay.
Also, I would try not to discuss the legal matters as much as possible. I would refer him back to his lawyer and let the lawyers do the work, after all, they are getting paid to do so. Try to remember, you can't have a rational conversation w/someone who is emotional and bouncing off the walls. The more you attempt to explain things, the more he will become angry and irritated. Best to keep conversations short and to the point...as their emotions are all over the place.
I know living w/a MLCer is difficult. I've been there and done that. It's not easy especially now that we are in a major health crisis all over the world and we are having to share space w/them or dealing w/them on a daily basis.
Sit quietly, the answers will reveal themselves when you least expect them to. The past is gone, the present is a gift and you need to focus on today, allow the future to reveal itself when it is ready.