What I've learned is that Dementia is not a diagnosis. Did you know there are 85-90 different conditions under the "Dementia umbrella"? It is true that 50-60% of cases are in fact Alzheimer's. Alzheimer's symptoms can last from 8-12 years. However with Vascular Dementia, for example, symptoms can last from 3-30 years. Whatever you are dealing with doesn't just affect that person, but the life of the caregiver (or family) also. But, there is life under the umbrella you are (all) living under.
Changes are constant but YOU have to adapt to the changes. Your loved one may not be able to see any changes in themselves OR they may be aware of the changes and afraid to acknowledge what these changes truly mean. Or they may be like my loved one and be aware something is terribly wrong but have no idea what it is or what to do about it - and see others as treating them very differently, which makes them angry!
You, my friend, are going to have to enter the world of your loved one. Slowly but surely. Don't expect them to be the person they once were, to come back to that person because they won't be able to. But you can travel with them on this new path. With patience, understanding and maybe even a little laughter... In the words of Teepa Snow, "Dementia is terminal, but so is life."