@Aki Heiwajima like chapters 20-28 (i think. After the thugs happening in Dan'a house), Dan felt extremely grateful to Jaekyung. Even Dan himself thought something in style "Even tho he was being mean and harsh towards me, I still cannot but feel grateful to him doing such a things for me even tho he doesn't have to." And that's prob from it. Because Jae has helped Dan many times and probably (theory) Dan never recaived any help like this and made him build deeper feelings for him because of it.