I'm so confused as to how people are related. The guy who got a part of his thigh cut off has a dad, right? Then…
Yes, the head of the thugs is the boy's father, and his mother is that lady you're referring to. Those two have a secret relationship and it seems nobody knows that she's the boy's mother.
I think she's trying to get something from the man she's currently married to.
Also, seeing Pi Hanul and Kim Suncheol from Study Group made me giggle a bit.
I think she's trying to get something from the man she's currently married to.