I can’t answer your question, but think it’s wonderful to have shared 14 years together. My brothers boxer had dementia, and felt he was too distressed. However I had a thought about the behaviour, because I had a cat who acted like this... circling, wall staring, and it wasnt dementia, but in fact was detached retinas, causing bits of vision, and resulting confusion. The vet said that she must be desperately unhappy, and at 18 yrs, it wasn’t fair, and there was no treatment.
I do feel for you, it’s very difficult.