I don't understand why they treat Ingo like a parasite. He was brought in as a child and really thought of Jung and his father as family. He was a shit head, sure, but he was sincere in his feelings and worked hard on his art. Then the guy he saw as a brother turned on him. Of course he thought Jung was behind the hand incident after he witnessed Jung's scheming. And honestly, Jung seem to have fanned the flames, just has he did to poor Seol (who never did anything wrong to him! He just disliked her for absolutely no reason). He gets somewhat of a pass because he was a child and seems to have had a shitty upbringing, but still.
They keep implying he's a parasite, when he just left and lived his life away from them. As far as we know, he didn't have any contact with Jung's family in years before he first appeared! He didn't even want of the father's present. He was abused and then used by Jung's father. Sure there might be the aspect of family that I don't understand very well as a non Korean, and him abandoning Inha (as a westerner, I don't see the problem, at her age she should be independent anyway).