Didn't want to read and run. DH has long-term mental health problems.
This is an absolutely crap situation. I am going to post as if you are still able to get in there and support your dh, but tbh if he is refusing to do anything to make things better, you are stuck. There IS hope, there is always hope, but it is utterly draining living with a depressive. The person you fell in love with is still there, I promise you, but I can't promise you that you will see him again any time soon, and the only people who would blame you for not being able to bear it are the ones who have never experienced this. TBH there are days when I congratulate myself for every hour I stay married (not that I'm an angel myself).
Contact Rethink for you, they can really help. Do you have family support, friends? Is your dh OK with you telling people about his illness? It's really hard if they want it to stay secret, I would say it's pretty essential for you to talk, though it's fair if he asks you to choose carefully who you talk to.
Is he on meds at the moment? It sounds as if he could do with some just now, even if he is trying to stay off them. Call his GP and talk to them - they shouldn't give you information, but they certainly should allow you to give them informatoin.
DH appealed against the ESA stopping and though ASOS dragged it out as much as possible, giving him and us an absolutely shit six months, as soon as the appeal panel saw the paperwork, they reinstated him - dh never even had to go to the hearing, which he was actually a bit pissed off about in the end as he had spent months building up to it! I was relieved though. Ask your GP if there is any specific support for your dh for the appeals process from e.g. a disability adviser at the Job Centre?
If his parents make things worse (not necessarily their fault at this stage, whatever happened in the past) what about just going to phone calls only for a while. You could explain to them that your dh needs to stay very calm at the mo and build structure into his life. Or you could not tell them much but just always be not well, or too busy, to see them for a while. depends how you think they would react. Stay in touch if you can though. After a dire Christmas we have decided not to see relatives at that time next year. I wish we could, as I love Christmas. Them's the breaks.
The things that help dh most are exercise (whatever he can, even if it's only to the end of the road, but around 2 hours a day is best of all) and meditation. Routine, sleep, structure all help too. hth.