Holy crap, the ending was crap. This is a super bittersweet ending disguised as a happy ending. I felt so bad for Seo Jin. Ha Na only loved him in the end because some of Robin's side imprinted on him. If she wanted to be with me after rejecting me for my other personality, I would have told her to fuck off.
Considering the drama it brought for them, I'm sure it will cover that arc.
Probably cover the first 3 volumes or so. Volume 3 + the beginning of volume 4 dealing with the cousin. The main drama though will come from both of them not being very confident since this is new to both of them.