Like one of the commenter’s comment – the pale-haired vampire dude isn’t Jae Min’s rival for Ma Ri’s love, rather, the vampire dude is Ma Ri’s “competition” for Jae Min.
Interesting twist of plot, I would say. But seriously speaking, I think what’s actually happening is that Si Hoo (the vampire dude) is attracted to Jae Min’s blood which seems to have “tasty” scent. If you recall from the beginning of the story, Ma Ri herself was also attracted to the scent to the point of biting his neck when she was not able to control her urge.
Anyways, this series is getting even more interesting with the appearance of this male vampire. I wonder, will Jae Min get himself bitten by this vampire dude? Even better if Ma Ri comes to his rescue