Aisling, I would like to send you a magic cape filled with gentle hugs that will ease your feelings of despair if even momentarily.
I don't know what resources are available to you, but there have been several knowledgable responses and very thoughtful replies with good suggestions. There is no one answer for everyone, and you need to do what will work for you, not what you think others are doing.
Think through your options, what will work and what won't. Talk to some experts, advocates, ombudsmen who don't have a vested interest. If they do, their advice may be slanted in a direction that works to their benefit financially. It sounds like you need financial and legal advice. When you know what your options are, think them over carefully. Make an informed decision. Talk with you son, before, during or after the process, depending on what your relationship is.
Talk to your doctor about your exhaustion and depression. It sounds like you've been told that you can't take care of your OH if you don't take care of yourself. My initial reaction was that people didn't understand, but they did and their advice was sound. AD will swallow everything in its path, if allowed to do so.
You take your time it will be lovely to hear from you when your up to it. Grieving is a long slow process, I am having ups and downs but I find talking helps me, everyone is different but be assured we are all here when you feel ready.
Be kind to yourself, big hugs sent xxxx