Even if you've never seen a single episode of due South, even if you've never read any fanfic before, read this story. It's a spot-on portrayal of Alzheimer's and its effects on not only the person who has it, but the family who loves and cares for him. In this case it's Early-onset Alzheimer's, which is usually quicker to progress, and harder for everyone.
Lost, by Tara Keezer
Then listen to this:
Tommy Makem and Liam Clancy - The Dutchman The song and the story have exactly the same feel: Sadness, bittersweet memories, and through it all the joy of unconditional love. *wibbles*
No, really, read it. You don't need to know the characters; they could be anyone, really. If you DO know them, it's all the sweeter.
It's not long, and it's so very good.