Responses
From what I understood it may be related to his own designs and furnitures. Maybe he stole his designs which led him to bankruptcy and that too they were friends. It must have hurt. And his sister saw the accident happening. And her scream pulled him out of his shock and he could save yoosoo,
So in nutshell, his father cheated on yoosoo's father..he went to tell him and tge bookshelf fell on his hand olay so if someones know what was the cheating about? And why was yoosoo's sister involved?