Damn shame, this started out really interesting: The focus on nocturnal life, the relathionship between the two MCs and being a role reversal gender-wise, the budding relationship...
And now we just have our generic love triangle. I don't know whether the author is just lazy, or if they believe that a love triangle would increase its popularity, but it really disappoints me.
If the author really wanted to introduce more characters, they should have just introduced this girl as having a boyfriend already who is, unbeknownst to her, also a vampire. That could open up way more interesting situations/interactions.
I just feel harems and love triangles are way too constricting. It's the reason I avoid most harem stories and most shoujo romances -- once you've read one, you've read them all.