Yes, they found out about Hyesung and left her for lying. She was all alone just like how Hyesung had been for years since he was a child. Dojin could have let her taste of her own medicine but he decided to act like a backstabbing dick instead. She's sticking to Byul like a glue now because she has noone else.
When that bitch left him alone then she never thought about consequences
She just cared about good life
If she wanted she could've easily saved hyesung
But nope
Her selfish ass was enjoying new life with new family
Now how does it feel when that same family abounded her the same way
She's sticking to Dojin and byul now
She doesn't even have a fucking guilty conscience

For those of you who don't know what the grandmother did:
1- She abandoned Hye-sung when he was 5-6 years old.
2- Her husband, Hye-sung's father, was abusive but that wasn't the only reason she left. She found another alpha (female). She left Hye-sung for her new alpha.
3- She didn't say anything about Hye-sung to the new alpha because she wanted to start a new family. Hye-sung was nothing but hindrance for her so she kept him secret. (People tend to forget this part.)
4- According to her (I don't know if we can trust her words) she wanted to talk to Hye-sung after she left but the father convinced her that Hye-sung didn't want to see her. (a 6 year old boy ffs.) She said "ok" since it was convenience for her and never ever bothered again.
5- After so many years she saw Hye-sung with a crazy rich alpha and tried to meet him. She had the audacity to blame him for "not looking for her". Yeah, she said this.
Hye-sung decided to live his new life without the shackles of his past but i'm afraid Fargo wants us to believe she's not that bad.