Hello lostone. Sorry you find yourself here.
I don't personally believe that bomb drop has much significance outside of the person receiving in. I think of it like water coming to a boil. There is a transition point that we can debate about but there is also a clear before and after.
I'm just going to quote a bunch of horse$h!te. I'm certain you know it is horse$h!te but I also think having such hurtful comments come from someone you trust and value deeply does damage. I'm hoping to give you more confidence that these are impersonal and coming from an unstable person's fear and rationalization.
"said I never made him feel seen or appreciated"
"could not agree on shared outcome (eg work towards reconciliation)"
"relitigating long ago decisions (that predate us even meeting), monstering, unable to handle ANY responsibilities"
Basically every action you've described him taking.
I also want to say that the things he says are shockingly predictable. I myself received many of the same comments. Of course, "I love you but am not in love with you" is an all time classic, but others include: "I don't know who I am", "I'm numb", "I don't like who I am with you", "you should get a boyfriend". There are a couple of older threads with more of these.
Oh, also the burnout clinic apparently validated that his problems are all caused by our relationship and recommended that he should get on DATING APPS
Why do you believe this? I don't. There are so many hinges. Did he tell them honest, accurate, and sufficient information? Did he hear their response without filtering? Did he relay their response faithfully and without manipulation to you? Do you trust someone that sleeps on the floor so they don't have to decide which couch to get will be able to shuttle such emotionally charged information to you without spilling it all over themselves?
I know that the person I married is still in there deep down
How do you know this? I don't mean to imply they are an alien, but speaking just for myself, I am not the same person I was when I was 20. That might sound trite. Who we are is emergent and that while I still care for my ex, I don't believe it was helpful for me to hold on to the hope that she was going to travel back in time and be who I remembered her to be.
Again, sorry you find yourself here. This is a tough time but you will get through this. Take care of yourself and your children and the rest will take care of itself, eventually.
EDIT:
If the wound is relational, surely that means that the repair is relational?
I agree, the repair will also be relational. You are willing to show up but he is not. The relationship pops out of the interactions between two parties. It cannot exist if one party is not breathing life into it. It is out of your hands, unfortunately.
What I guess I really need to figure out is how to deal with this limbo and if this really is MLC or if it's just the end of my marriage.
I found that rational understanding was greatly overstated. Let's imagine you have this knowledge firmly in hand. Now what? You still have the emotional turmoil and the practical day-to-day of reconfiguring your habits. With time, whether or not it is a crisis or clarity on his part won't matter much. A rose by any other name, so to speak.
I've done the quiz and I've worked through the free course and I've read and posted in the facebook groups but he is resolute that our relationship has caused his "burnout" his word for what's happening to him and that while he cares for me and will "not rest if I'm not happy" (wtf) he "cannot" be in a relationship with me. He's trying to tell himself that Divorce is a good outcome for the kids too and outsourcing having decisions made for him to me meeting someone else which I loathe.
If you think of him like a small child instead of a fully grown adult man, it might help. He has no clue what he is talking about but the words sounds cinematic. The words sounds heroic. They don't portray a man leaving his family because of feelings inside of himself he's unable to sit with. He is spinning a fantasy because it provides escape. What is he running from? Who knows.
It's just this, for a while.