OP, sometimes we just have to accept that with the best will in the world, you cannot make something happen.
It cannot be the case that you are the main reason he's in work, it is more practical and better for you to let him fall off this particular cliff, and then, having surveyed the wreckage (and gone on UC, and had treatment for his anxiety) decide what to do next.
Get the book 'Let Them' and read that.
Mums can't just support people out of illness, trauma, MH conditions- people on Mumsnet often think if you just try harder, differently, more, then you will be able to solve your children's problems, but that's not always the case.
At the moment, the evidence is telling you he can't cope with work, you can't cope with him working and his work can't cope with him either which is why he always loses his job.
You need to listen to this, give him respite and get him on UC and support him to make a plan for himself.
For ND people, this can involve a different type of lifestyle than those traditionally provided for those without ND. He might flourish as a volunteer in a gardening space, set up for those with ND or other issues. He might do very well with others with ND. He might do better once his nervous system has calmed down as he can't live with that level of anxiety all the time. He might do better on a different medication such as Effexor which helps with anxiety as well as depression, and isn't a beta blocker and doesn't affect BP.
This is not the end of the road, it is a pause. See it as that, give him a big hug and allow him and you to take stock and rest for a while whilst you think up Plan B.