The 64-year-old star - who married German publishing heiress Nora in 1979, and became stepfather to her daughter, The Slits singer Ari Up - first revealed his wife's diagnosis last year.
Now, he has compared her condition to a "permanent hangover" and admitted "it gets worse and worse".
He said: "I suppose her condition is one of like a permanent hangover for her.
"It gets worse and worse, bits of the brain store less and less memory and then suddenly some bits completely vanish."
John revealed how impressed "alleged experts" have been that she still remembers him, and he suggested "a bit of love goes a long way" when he comes to taking care of her.
And he insisted he has no plans of putting Nora into a home in Los Angeles - where they both live - despite the strain her illness has on both their lives.
The 'God Save the Queen' singer added: "I am under lockdown anyway because I am her full-time carer. I don't need to go out and socialise with buttholes."
However, he is "furious" that gigs have been cancelled during the current coronavirus pandemic as it means he is losing out on money after Public Image Ltd. had to cancel their touring plans.
He said: "There's been no income so I am f***ing furious and none of this, let me tell you, I don't care how communist you believe you are, none of it works without a penny in the bank."
