I was thinking that the father may have not let her visit when she tried to again and by the time she got to, Hyesung already left the house
Nah. she didn't want the "burden" of raising Hysesung alone or hinder her chance of "happiness" i.e finding a new partner, by having the kid of her previous marriage as extra baggage. She's a coward and a POS. She left her son behind so he could take the place of being an emotional punching bag or prostituted by that POS father. What a bitch.
Maybe
That could be also true
I feel like the mom ran away bc the dad is an ass and yk how the story goes.. she disappears for a peace of mind and then disappears for to long so she feels like she's not worthy of being the mom she should have been and hides away