I think it has less to do with the plot twists and just the SEVERAL flashbacks paired with a lot of open-ended conflicts within the story (it feels like we've started several storylines and haven't closed any of them). We don't even really know the characters' relationships with each other (MC's relationship with Sunbae went from an implied crush for the last 60 chapters to an apparent ex-relationship. Also, the ML who played/toyed with the MC for most of the story hit us with the "you were my 1st love" and then never elaborated??) and because of this, it's hard to be invested in any of it.
And the Mc's brother, just randomly pops up occasionally is he dead? is he not dead? is the MC responsible for it? when did this happen? He was apparently close with the ML, how is that relevant? Was the possible dead brother plotline actually needed? Where does it fit into the whole thing? (Is he in the hospital and that's why the MC got into porn? because he needed the money?)
Why these korean manhwas are full of plot twists and a lot of confusion for the readers? At this point the author seems to be desperately trying to create sth to surprise the readers which isnt working. So boring!