I think you've explained that really well. Yes, you might feel things more intensely - apart from anything else you have one T and he has more than one client, and you need his help so of course your emotion is different. I very much doubt though that he'd walk from this and never look back. He has an investment in your relationship too. He sounds like a capable, competent T, albeit out of his depth here, but he's working in it. My guess is that he would feel a huge sense of disappointment, upset and fear at not being able to resolve things with you, and those feelings can be career changing.
I wonder if you can think of the feelings of instability as being natural at this stage? You're going through a huge rupture with your T, boundaries are being redrawn and you're looking at your therapy and the therapeutic relationship in way more depth than would be the norm. So, everything is shifting and its natural to feel unstable, wonder if it'll get back on track and to not be sure what that track will even look like.
I know you feel threatened by his supervisor saying that if she showed what you'd written to her supervisor, she would recommend ending the relationship. That does sound very scary and can leave you wondering what the hell you're putting yourself through this for. I can see why she would say that though because while raising issues that aren't ok, you do need to think properly about what you've gained from this relationshipbefore and what you'd want to keep. Yes there are things that need fixed, but if that's where you focus most of your energy then that's all you'll see, and you need to move forward. Resolving the stuff that isn't ok may be a slow process, if it's been your Ts way of working then he needs to learn new habits, read up on theory, change his process work and that can take time for him to become comfortable in new ways and old habits do die hard.
I need to be clear that I'm not saying you're wrong to identify issues, or that you need to put up and shut up - not at all - but if you can identify what he's done that has been helpful, it gives him a place to work from at rebuilding things. You also need to decide how important it is that he or his supervisor actually says "yes, this hasn't been good", as opposed to working on making it better. I guess what I'm saying is that he needs to be able to see a way back into the relationship that will be ok for you both and give enough wiggle room for him to feel safe trying (and getting it wrong) and for you to be able to say, in the relationship, that something isn't working.
If there are bits that are key, eg working within your window of tolerance (however small that might be) and making sure you're safe before leaving, I might take control of that for a while. I actually wonder whether it's productive of you to be trying to do therapeutic work with him just now rather than spending time with each other rebuilding the relationship. I know for me the sessions where I feel I've not got into hard stuff, spoken about trauma or triggering stuff have maybe felt less productive at the time but have built a very strong relationship with my T. Maybe lay off the stronger stuff just until things feel more stable - remembering that stability is key to any trauma therapy and that means stability in the therapy.
Also have a think about that promise not to abandon you. I really struggle when Ts say that because they actually have no control over whether you feel abandoned or not. Your T doesn't know what will come up in his life that might mean he can't be there for you. So maybe look at it as he wont intentionally abandon you (if you think that's the case) but that endings come for all kinds of reasons. Ending doesn't mean abandonment, it means ending, though it can feel awful. The thing about abandonment is that it puts the cause of the ending at your feet when things do just end sometimes. If you can't work through this and it does end, it's not because of anything you did or didn't do, and not saying anything was wrong would have been a lie, it's ok that you did it and it doesn't mean he'll leave you, though ending might be a natural result if the relationship can't be fixed. If it does end, it'll be hard hard work to get through, but you will be ok. I know you don't think this, but there will be a way through it.
Last thing from me, I have no sense that despise your T or want their career to end, I admire how much thought and work you've put into trying to find a way through this and think you've been pretty respectful in very trying circumstances.
So, I feel like I've written a lecture, as ever, take what's useful and dump the rest.
