I am not sure but I think he was in a situation where he was force to do something bad and that made him bad person, maybe.. He is an ambitious and self-centered.. He is being possessive and obsessive with do hee..It was shown in ep. 15 to 18 that he is making up stories, acting pitiful to do hee, willing to put others (including himself) in danger to get what he wants specifically to get do hee back again, and he is even trying to control some events and people to make his plans work. He is also stalking do hee.. However, it was shown in previous episode (I can't remember what episode is that) that it seems like he is suffering from heart related disorder and he was trying to hide it.. In ep. 17 to 18, they gave us glimpse of what he did to keunee (the homeless) in which, he reported that a patient with depression committed suicide using the prescribed medicines by his Psychiatrist (keunee) and he made it look like keunee is the one should be responsible and to be blame to that suicide which led to the fall of keunee.. I don't want to conclude that he is a bad person because the whole story behind of all his actions is not yet fully shown and I think he has a reason (maybe) that drive him to do everything he has done before.. - just an opinion base on what I observed in the drama..
In the Monday episode Keanu said that he was a patient who lacked of love from childhood so he became obsessed with Dohee because she used to love him very much at that time.
