afaik, hyesung's parents are divorced. his mother run away and left him with his abusive father. eventually, the mother seeks her ex-husband again so he can sign the divorce papers and get remarried. so his parents remarried and hyesung had to live a life poorly bcs he ran away from his father when he got older.
when hyesung's father found out that he married dojin who's rich, he tried to find him and made a scandal. after that, his mother found out about him also married to dojin due to the leaked photos of them circulating the internet. there's a scene that they both talked but with closed door as hyesung didn't want to see his mother. they talked and asked her why didn't she find him. and his mother replied that hyesung didn't even tried to find her either which is such a bs reasoning imo. after that, hyesung didn't want to talk to her again and cut ties with her. but yeah, not entirely as both byul and dojin still had a communication with her.
hey guy... I forgot the issue baout the grandma, can someone please tell me what happened? (I don't wanna re-read)