Who are these troubled people?: The Vegetarian

I can see, reading the second section of Han Kang's The Vegetarian, that this books, which comprises three long stories published separately, is in fact a novel or something like a novel; the 2nd part, Mongolian Mark, takes us a few years later in the lives of the characters. The troubled young woman who seemingly on an impulse decided not to eat meat, leading to a crude and cruel family intervention (father slapping her and trying to force fee a piece of meat), a suicide attempt, a hospitalization, and some bizarre behavior (sitting naked in the hospital lobby), is now divorced from her boorish and narcissistic husband and, several months out of a psychiatric hospital, living alone and trying to rebuilt her life. As in part 1, however, she is a secondary character (although the title character), and both sections are told from a male POV - the first, that of her then-husband, and the 2nd from the POV of her brother-in-law  (sister's husband), a video artist with a strange obsession: He is deeply attracted to his sister-in-law (much more than he's attracted to his wife - odd, in that the vegetarian's husband made a point of saying how his wife was entirely ordinary in appearance - taste differs, of course, but there seems to be a theme here of mismatched mates). In this section, the video artist, seemingly trying to help out his troubled sister-in-law by visiting her and solicitously bringing her fruit, persuades her to pose for him in a video. He begins production of the video surreptitiously - it involves his painting her with a network of floral designs. Though in general she is shy and uncommunicative and seemingly repressed, she really likes the designs he's painted; in the 2nd shoot he asks another artist to join them and he paints him, too, and then asks them to have sex while he films - the other artist protests, angry that he's been duped into what appears to be a porn film, and stalks off. So the video artist has himself painted w/ floral designs, shows up at his sister-in-laws, and they have sex - all recorded on his camcorder - which of course his wife discovers. She's furious at him not so much for his infidelity as for taking advantage of her obviously mentally unbalanced sister. Well, the whole story is mentally imbalanced - I guess it's all possible, anything's possible, but it's unlikely and unpleasant to read: Who are these troubled people, why are they so cruel to this vulnerable young woman, where are we coming from where are we going?