He knows that Leray is a vampire but is still infatuated with him so I don't think that's the reason.
oh..I kinda thought Leray tricked him into thinking he was human/they share this thing about wanting to kill/experience on the blond vampire.
Didn't he say in this chapter that "Professor Bian IS the vampire Leray...who wants to destroy the world" (I just checked again and that's a direct quote after he has that flashback of sea telling him love is weak on page 6 if you wanna check it out yourself) but I do believe Leray is manipulating and he also probably realises it to a certain extent.
why do ppl hate the black haired kid sm?? I understand hes just smiling at the sideline while ppl are being tortured but high chance...he was taught that vampires weren't people and deserved all of this