stop trying to understand. She leaves for her sanity, period. Now she has made him understand that she will never stop him from coming back to her. He just has to go to her countryside...
Most people don't understand this drama. It's normal, you have to have experienced a lot of things to understand it. I understand each character very well and I think the script is clever. The drama takes us where no predictable drama before could. Anyway, Moon Ga Young hinted that it was a happy ending, so enjoy :)
Be careful not to scatter too much in the story it's true that it goes all over the place but the cast is excellent with him, and she makes efforts of facial expression lol
K-Drama 
1 
In any case, the whole atmosphere is interesting.