Gateway Parts - What is the movie "The Notebook" about and what are the sad parts in it?

What is the movie "The Notebook" about and what are the sad parts in it?

Don't copy and paste a summary but tell me in your own words what it is about and what parts make it really sad?

The Notebook starts with a an older gentleman reading from a notebook to a lady in a nursing home-she has Alzheimer's & doesnt know who he is. You find out that the old man (noah) & the old lady (allie) are lovers, who while the odds were stacked againsts them, fate brought them together. The Importance of the notebook is that Allie has alzheimers & when Noah reads from the notebook (the story of their romance) it awakens her memory & she is able to remember. The sad parts are : well obviously Allie having Alheizmers & not reconzing her husband or kids. When Noahs best friend dies in the war. When Allies mom brings her to see her old "summer love" & explains to her why she chose her father. hmmm...what else, when Allie leaves her fiance to go back to Noah.