I'm so sorry. I don't know if this helps you any.
The only times I dealt with something like that?
1) A past BF who was doing that kind of black hole of doom thing. He wanted to "act like a man" and not tell me what was going on with him on the insides. Fearful that he would look like a wimp. When really? I'm not
blind. SOMETHING was going on with him. And leaving me in the dark about it? Was basically pushing me away. Not allowing either mental intimacy nor emotional intimacy. He preferred his false pride thing to actual relating with me.
When things became the CHRONIC black hole of doom? I asked him to see a doctor. He refused. So I walked out. I don't think mental health people are bad people. But I have my OWN mental health things like anxiety. I cannot be around UNMANAGED people.
Again, I didn't leave because he had depression. I left because
he didn't want to deal with it, manage it, or talk to me. Many gf's later who left him for same reason? Unmanaged depression? He called one day from nowhere to apologize and tell me he FINALLY got therapy and was working on getting better. While I was glad for him, I also thought "What a waste of so many years in service to your weird false pride. Could have gotten help sooner!"
2) My DH went into a deep funk when his mother died. Other deaths we'd been able to grieve together and support each other through it but I think he just went weird when it was his MOTHER. I get that is tough, and I gave him some time and space. But DH was really going into a deep grief weird.
So I had to have a talk with him about seeking grief counseling. And talk to me about what we could realistically let go in home routines, what could be on my plate to clear him some space TEMPORARILY. And how soon he'd be able to participate in family life. Because he couldn't just check out forever leaving me with the care of everything else all by myself... PLUS tending to him in his grief. I was grieving my MIL too.
For myself? I went to talk to my friends (male and female) for extra support in this weird time. I lined up helpers with the house. I dropped stuff I could drop. I dealt with my grief stuff. I stopped talking to DH in words about anything important and changed to email. Because words weren't going in. Email? Sometimes yes, sometimes no, and at least I could pull it back up to show him *I* was holding up my end of agreements. There it was in the email with a time stamp.
That actually was a turning point for him and made him see that I wasn't being unreasonable or a nag or crazy. I really did email the thing when I said I did. It was HIM who was off in grief land and not parsing things well or meeting deadlines or being responsive in a timely manner. He got better little by little and I think the biggest turning point came when we had her buried properly with a stone and everything. CLOSURE.
You can offer to help BF make a doc appointment or even give him a ride to the doc. Reasonable and rational requests might be ok. But if he gets a dx? You can't make him really work his management plan with his doc if he's just not gonna. Or make any of his other decisions FOR him.
It may be that this up and downy thing with the LTR is better just " officially broken up" once and for all so he can get over it once and for all. Rather than dragging on and on. But that's not behavior you can do for him. He has to make that call.
If he's going on about "how he just has to suppress who he is and be a normal person?" Maybe he means he's realizing that he might WANT to poly, but he's not got the skills to be ABLE to poly well. So... maybe it's not just letting the LTR go. But letting you go, and the whole poly thing go. He has to do his own soul searching and figure out what he wants.
If you need a break from the negativity and want to move out? Move out then. Have your own space so you don't have to live in a doom cloud.
Maybe it will be a wake up call for him. Maybe it's not and he continues to sink in the mire. But you do't have to sink too just to keep him company.
If you have done what you can and he will not even take a little personal responsibility? It has become time to let go of the rope?
Let go of the rope.
Galagirl