@Lan Anh Nguyen what you said is right that he treat Kwon Ido's suffering as a tantrum but in my opinion i think that he was really dissappointed because kwon ido had given him all he ever wanted but then once his memories of past life came back he left him saying that he can be independent but at that point Ido was the only thing that sejin had which made him feel betrayed. And Ido had not even given him the choice that he can stay with him after apologizing which probably made him feel that this like Ido used this new life to redeem himself for past life for his own satisfaction and not for sejin. And in my opinion this all made sejin not believe Kwon ido's suffering or acknowledge it and becoming confused about it.