This is for all the watchers just starting or in the middle of the show. This drama was AMAZING and worth the watch, definitely! But pretend episode 16 doesn't exist for your own sake. If you're okay with open and wholly unsatisfying endings, give it a go, but if you're hoping for an ending fitting the rest of the tone of the drama, pretend the last episode isn't canon and that the last 2 minutes of episode 15 aren't either. Stop when Ja-Sung and Young-Won are smiling happily on the couch together. I beg you.
What happens at the end of 15 and all of 16 if you're curious:
Ja-Sung shows the audience a picture that shows Young-Won's father is the man who cheated him out of his money. Young-Won finds her dad and brings him home, then takes Ja-Sung on one last trip to leave him with happy memories so she can break up with him because she can't handle the guilt of Ja-Sung thinking her father ran off with his money and was feeling suicidal afterward, despite Ja-Sung telling her that the misunderstanding is cleared so it's "water under a bridge". Young-Won disappears for 3 years and has a new job at a different magazine (after running off and leaving Ja-Sung heartbroken and probably suicidal again since Shin Gyeom won't leave him alone) and she and Ja-Sung run back into each other after returning to the spot they took their trip for a business deal. They then go to Young-Won's house that she built for herself, and that's how it ends. They aren't shown back together. Are they friends? Do they re-kindle the relationship? Who knows. It's horrible and a waste of time. The happy ending happens before the father's character is introduced.
What we're going to pretend is canon:
Option A) - All of the above didn't happen. Ja-Sung and Young-Won get married and years later they find the photo. Ja-Sung explains what happened and Young-Won agrees, since she hates her father for running off and leaving her mother and her to struggle like a deadbeat. The father is probably dead, but maybe not. Ja-Sung continues teaching Young-Won about real estate and she still builds her own house. They become property moguls as a nice couple hobby of theirs. They have a happy life and many children together.
Option B) - The end of 15 and the first half of episode 16 is canon. Young-Won is willing to accept that Ja-Sung views the situation as "water under the bridge" as he said. No hard feelings, and in fact Ja-Sung and Young-Won's father have a nice little catch up and the father apologizes and explains. The father gets to be there at Ja-Sung and Young-Won's wedding. Ja-Sung also continues teaching Young-Won about real estate in this version, and they still become property moguls as their couple hobby. They have a happy life and many children together.
I personally prefer Option B. Otherwise the father seems kind of like a man in the refrigerator, but if you think the dad sucks then by all means, Option A is there for you, too! Happy watching (just not the last episode)!