Yes, communication is key!
I am sorry for the struggle you both are facing!

I hope the recovery effort for your partner comes along well. When we are burnt out... we don't even have the energy to enjoy the things we love. EVERY thing takes some sort of effort. Even plants will die without "rest"!
It took 40+ years for my husband to START healing from his family trauma... His aunts, uncle's, and grand parents who he was left with in Korea for 2 years at the age of 10 while his mother came to the US and spent the time to immigrate LEGALLY had issue with his father and took it out on him (my hubby) by telling that his mother was never returning for him and one day he came home from school to find them eating his PET dog and laughing about it. Making fun of him for crying.

Oh boy the fall out... abandonment issues and others that were stuffed down and surfaced every time we faced difficulty. And I see and feel his pain first hand. I hurt FOR him. I cannot discount how this has effected him... Finally he see's it's not what happens to you that dictates who you are... but how you react to what happens. Obviously his pain is real and justifiable. BUT he CANNOT continue to use that as an excuse for his actions TODAY. He MUST choose healing instead of reliving that day over and over. I understand this is MUCH easier said than done. Time does help wounds heal. They still cause pain at times but it doesn't have to be in constant control of your (our) life. Religion or not... what is always on your mind IS your God. (general speaking and sharing, not actually pointing a finger at you). As a man thinkith, so is he... Thought leads to action. It is SOOO hard to get out of a spiraling mindset.
It is NOT easy to have a good relationship, you are correct. It is heavily impacted by our relationships we had from the day we were born.
Please know... I'm not trying to push the Bible on you... just share my understanding a little. One interesting thing it says... man and woman are to leave their mother and father and cleave to one another. And in ALL the world... I see most animals reach a teen phase where they buck up and venture out on their own... to become their own person/being. To use what skills they were taught but choose their own path/new family... Your partner sounds like an amazing person, who with good support will very likely overcome this. Recovering from burn out, something my husband and I are just starting to... boy can it ever be hard... exhausted, beaten down by life, even JUST breathing takes effort... I remember!

And some trauma is like you have been to war. People DON'T come back from war happy and functional. They come back stressed and shell shocked... ducking at every flying thing expecting a bomb. They don't know how to decompress or how to connect with "civilians". They see every relationship as one that can end in tragedy so best to build a wall. Plus they don't wanna share their trauma and have us feel their hurt. Often presented as anger. Everyone will have their own timing and differences. Continuing to provide a safe place without flash bangs or explosions going off all the time keeping the warrior on edge, where their fight or flight system can get a little reprieve should help. But they may still react when a car backfires... it's a natural survival instinct...
Ahh, "family"... what I learned and the movie Ice Age (I think 4) really brought home for me... I had a birth family. My parents are heroin addicts and my brothers and sister followed the path of having their kids taken to foster care. They ALL call when they want something expecting me drop my life and even to choose them over my husband. But they aren't showing LOVE (remember the definition I posted)... If blood is thicker than water... why do they never choose me? With family like that who needs enemies? Well, we can't choose which family we are born into... but we DO choose the family we pursue... As an adult I realize the friends I keep ARE my chosen family! That used to hurt... and it still does a bit. It's hard to realize you lost your mom... even though she is still alive. Chickens have been my recent past drug of choice, and they are working to a degree. They are ONE tool in my box towards recovery. Dogs also really helped a LOT as they are very loyal and don't hide their feelings or fake it.
Listen.. I'm going on and on here... and I'm not trying to not hear what you are saying. I do here you loud and clear is the point I am trying to make. And you are not in this alone even when it feels like it.
That is so awesome! And it really counts. I believe he will have healing and be blessed beyond belief. Sounds like he is trying. I love when people want to be better because THEY want to.

(I know it is still a process though, sometimes slow.) You sound like a very smart person, and caring. I hope you both hang in there and grow stronger together. Talking and listening is a great start, HEARING and understanding, possibly even better. Thank you for sharing!
Honestly, if you can get past all the
people telling you what to do and how to live (a MAJOR drawback for Christianity)... maybe by realizing they aren't Jesus and may not have a clue... it really does help to have your life/heart filled with the Holy Spirit. I don't care what people say, I care what God says. And my take while just as black and white as many other hypocrites... knows the peace that comes from knowing.. I have been transformed by this world and NOT conformed to it.
I strive to let my life, (chosen) family, and marriage be a living testament to the power of God and His healing. I wish I could share the JOY with everyone. Happiness is fleeting but Joy is everlasting. Trust me, I have NO room to tell you how to live! And according to the Bible most who think they can pluck a splinter from your eye, need to remove the plank from their own first.