To me more than faking it, it looks more he is someone suffering from severe split personality that he developed…
What is oddly is that why would jae beom jump off the building althought he feels sorry in killing wonseok if he really the one killed wonseok. Why does osung always ask jae beom and even to jae beom mother if jea beom tells something to her or if he remember something. Osung also is sus.
Look like jae beom osung wonseok and pianist are close. Its odd when osung told jae beom that not to mention wonseok anymore and osung shows some polaroid photo of jae beom and wonseok he said that jae beom have it before he jump in the building of his parents. Osung is odd here i think he could be the killer that push jae beom in the building and jae beom lost his memory. Osung make up story and tell jae beom that he try to kill himself any way we dont know the reason why jae beom jump off. It look like osung is trying to cover up something and frame jae beom or either he was frame.Anyway we will find out .