Wow, this sounds incredibly hard. I'm sorry.

The best thing you can do is take care of you. That probably sounds terrible, but I think it is true. Someone who doesn't want help or will not accept help, can't be made to. I speak from experience on this.

But you can get help for yourself to make yourself stronger as you deal with this. Maybe he draws energy from you & if that is the case, you need to rebuild your own stores to stay strong for him. And find the strength to be happy for both of you. It is a good way to use the time that he chooses to shut you out.

I hope he will be able to lift himself up and out of this someday, but in the meantime, please, take care of you.