That would still be regarded as child abuse. I wrote earlier in the comments that a possible reason for his trauma was if he witnessed his mother (who idolised and was dependent on) having sex or being assaulted, presumably by her husband/his dad seeing as he was already shown to be violent and in his mindset he would get to show authority by forcing his son to see such a scene, or simply by allowing his son to see that scene which would still be regarded as abuse.
I could be completely wrong though, who knows. If anything it's good to have a not so predictable manga that has inspired so much analysis.
so basically Sangwoo has “mommy issues”.(?)
Yup
Ok this is my theory:
I start thinking that maybe Sangwoo was not victim of abuse as many are stating, but he witnessed his mother having sex with another man. Moreover Sangwoo said that when he was young he was too honest: I think he went to his father revealing what he saw. That "is mom disgusting?" in his dream could be a memory of that moment: she thought he did that cause he found her disgusting, but probably at the time Sangwoo was just clueless. But his father was violent and almost for sure beated her up more than usual... Sangwoo felt guilty and took the knife either to kill her (so to free her from suffering) or to kill his father, who had just killed his mother in an excess of rage. Up to now Sangwoo has admitted having killed his father, not his mother.
However since his mother's death Sangwoo has been searching someone who could replace her in loving him in a "pure" way no matter what his true nature was... But he could only find lustful girls attracted by his appearance and asking for nothing else but for a sexual relationship. Since they remembered him of the sinful side of his mother he killed them. And we know the only man he killed before meeting Bum was his father... the others were all girls.
Now, in Bum, who declared to love Sangwoo in spite of being almost killed, he saw the loving side of his mother and the fact that Bum's a boy may be the reason why Sangwoo sees his mother in him (on a spiritual level) but accepts to have sexual acts with him without killing him right after, since Bum does not resembles Sangwoo's mother on a physical level. I mean it's true that Bum may seem as a girl since he's thin and small (otherwise Sangwoo who is straight wouldn't do him), but he's still a man and so he's different from his mother.
So complicated
This manhwa is driving me crazy too