First I want to acknowledge the writers for tackling a difficult subject of Alzheimer.
Second.. Hong Je Yi.. Watching her act was amazing. Not for one moment I didn't feel that she was acting.. As a young child of 6-7 years, she brought out moods, and was a natural actor. In my view, she carried that 2nd half of the drama.

First 8 episodes.. All I can say is: "what the hell!!". The husband decides to be a martyr and he forces his wife to have an affair because he loves her deeply. This is one thing I don't get about Korean dramas.. "I really love the other person so much that I will create misery for them by sacrificing myself!!"
Also, the director or the writer creates more misery for the viewer by postponing the inevitable which was to have a meeting with husband & wife and wasting footage by going to grocery store or fishing.

Ok.. Let's go on to the next half.

After the wife deduces that her ex-husband has an illness.. her dearest friend would rather watch her go through misery than to tell her the reality. I really don't consider them to be true friends.
I do acknowledge Kim Ha Neul acting because there was one tender moment where I truly felt her pain and the discovery that she had been living a lie. That brings up another point "What's up with MOMs in Korean Drama". .. They seem to be just present to F*** things up for the main character.

Finally after trudging through the whole drama, the ending just fades. There was really no conclusion. To me it seemed that they lived happily ever after..
In conclusion:
The story telling was very poor.
The drama was very infuriating.
The character's behavior was circumstantial driven. The question I kept asking myself.. How are the lead characters transforming and growing?

Should you watch this drama? .. Maybe if you don't have anything else to do.