Responses
upvoting this bc finally a decent comment & who defo understand byul! ppl calling this betrayal doesn't sit right with me bc what does byul know??? he won't understand why his father hate his grandma til they explain it to him, bc for him, his grandma is nice & treats him well... hope ppl would cut him some slack, he's still a kid

As Hyesung mentioned "Byul is a good kid". Yes, Byul is a good kid that sees an elder woman struggling and being abandoned. It is easy and human to emphatize with old abandoned people. He does not realize everything that the woman has done to his father, because that happened long time ago and also because he is a teenager. In that case, his parents should have explained why they cut ties with her and the pain that she caused the father/mother (I don't know anymore).
People asking for Hyesung to abandon Byul, sorry but I don't approve. In that case, Dojin should be responsible.
Should she be forgiven? No. But there should be a better communication in the family.
I had a similar experience as Byul but at least they informed me about all their problems beforehand. Of course this is fiction and miscommunication is the best way to cause drama and make Byul be with Siwoo.