Responses
Something bad def happened in the room why else would Jun be scared of it now when he wasn't before, and Yeonwoo keeps saying that they found out "the truth" there (??). I thought it was just psychological, or dissociative identity too.
But what I can't figure out is sensei saw Yeonwoo talking to his evil reflection, and Jun's friends witnessed the mirrors shaking. We also saw Yeonwoo by himself talking to his agent about the missing reporter so I think he's real, that would be really random for Jun to make up.
GAH! I need answers!!

My theory is that jun killed yeonwoo's parents and he doesn't want to admit the pleasure he got from it yet, maybe he is psycho. I even think that yeonwoo isn't real sometimes, or actually never met again after the incident, that he's just a part of his imagination from his hidden side, but well he could be real too and devoted to him because he saved him from his parents. But i can't explain the evaporation cases yet and i dont think this has a supernatural twist. I think is just how jun's mind makes everything up to cover his dark side, i don't know if it's his yearning for killing other people or how he .explains other murders that he already commited.