This is yaoi. Unfortunately korea never invented a korean word for this genre like Japan did. They just slapped bl on all works, basically. And because there is love in the word it gives the impression that it is a romance genre. Meanwhile yaoi is so broad it doesn't, it is almost like a demography that can have romance as a subgenre or not.
Would not say this is that well written tho, but I read the novel like 2 years ago so I might have forgotten some stuff

This is not a romance. It is a twisted story that is devoid of human empathy and rooted in a perverse sense of redemption. This is a psychological horror and should be for 21+ if you’re under that age wait and read till you’re older. The art and storyline is incredible and disturbing in a horror format. Howver, their dynamic should not be glorified as a black flag couple.