After seeing the preview for episode 24, I'm so happy they're morally destroying her XD I mean, you marry the older brother but then you want to date the younger brother, what a stupid thing to do!
I completely understand that she uses everyone, but I feel she does have some affection for ML. She herself says that the protagonist is her greatest weakness because he's very kind and she knows they could always be together.
In fact, the series is good and with an open ending. Maybe one day they'll make a second season. PS: More or less in what year is the story set? Korea had a lot of wars.