People who are Seju fans seem to think that Seju is the one who's hurt the most among all the characters. How is her life? She is rich. She owns a company. What have her family done to her? They can't do anything to her. They can't command her to do housework. Her daily life can't be difficult like Cinderella's. All she needed to do is not to visit them. I'm not korean, I really have no idea about korean culture, is visiting family a must? I would say Seju is really bad at living her life.
Sumin dating Sungji and having Seju at the same time is wrong. If she dumps Sungji and goes back to Seju, it's also wrong since she promised her that she would try her best. Regarding Sumin receiving punishment, I think her having scars on her shoulder hurt her enough already.