OK Dave - I'm afraid that if you truly can't put your dear wife into Care; and you can't find the strength to continue to look after her alone, as you have written ; then you have just one choice before you go under. If that happens, you will not be able to take care of your wife as you would wish.
You must get some help! Otherwise, you'll not be of any use to her, and you will hate yourself.
There is help to be had out there, and you must forget pride, and ignore your wife's protests. Go out there and fight like a tiger to get help for her and for yourself.
If you can afford it, you might have to insist on a cleaner for a few hours a week.
If your wife can be coaxed into understanding that your work is suffering while you have to do all the housework, washing and cooking, she might agree that you need to keep the money rolling in, and that you need help in the house.
There are many excellent care agencies, with specially trained staff who will sit with your wife whilst you have a break; most will also do some ironing or light housework at the same time.
Social Services will possibly be of help there, and you need all the assistance you can get, to help you to be the best carer you can be.
It seems that your son and his girlfriend need a reality check too! A few home truths about just coming down for their meals might be in order. They need to get their heads out of the clouds, and either buckle down to help out - or get out and stand on their own two feet. You've got better things to do than cook for them.
I know that everything I've written has been mentioned by others, and you'll probably think, "what does she know" - but you need to take the initiative to reorganise your life before you go under.
It's a tough path you're walking, but there are others on the same road, and they all wish you well.