I'm confused too but it's cute lol
Taehyun, the blond guy is Hajin's cousin. Jaehyuk is hajin's friend. It wasn't explained yet how they met and why exactly is Jaehyuk so protective over Hajin (I mean apart from his love for hajin), but as for why he doesn't know that Hajin is a vampire, it's because they are only friends and Hajin doesn't go around telling averyone that he is a vampire. Jaehyuk is the one being clingy and protective, Hajin doesn't really seem to care that much about Jaehyuk so it's not like they are best friends, he has no reason to tell Jaehyuk that he is a vampire.
I read this in one sitting but im hella confused? Like, did i miss something? IK the blond vampire is hot and good but who is he again? I mean what's his relationship with hajin? A friend? Also what abt jaehyuk? WHAT IS HE EVEN. How come he doesnt know hajin is a vampire IM CONFUSION