Hedgehog, my advice is meant very kindly and to help you, not upset you even more, however I fear you will not like it and have a "yes but"..
Firstly, I am parent to Dc with SN and have a significant disability myself so I get the situation you are in. It is hard work and it is relentless at times, but the DC are here to stay and their needs will not change albeit it will get easier as they become older. Cling to that thought when you need to.
However. You and your DH absolutely need to be a team or you need to be apart. One or the other and you (and he) are going to have to CHOOSE which option you take. You cannot do this living together as you are. It isn't sustainable. Your posts about your DH do not change. He probably will not change, whether you separate or not. You need to accept this and decide what you want to enable you all to live in the way you should be living.
You are causing yourself needless angst and misery. Please DO NOT say you can't cope on your own. If you separate, buy in help or arrange access so you get a break. If he (sorry) died tomorrow, you would have to cope. For your DC.
I Worry that your repetitive threads will alienate your support on here as your situation is so frustrating.
Please Hedgehog, make a decision. Be a team or separate and parent separately. It may be he makes the decision for you. But you cannot carry on the way you are.
And remember, they will get older and it WILL get easier, but you have to help yourself now. It's in your control.