How would us humans understand, vampires aren't situated to understand that its kinky to suck blood and displays romantic connotations, actually that whole thought process is based off our own ideals of sucking blood is a form of kink. To them its just another average Tuesday, where everyone they see is a walking IV bag. Unfortunately, if we see 2 people potentially going out, and we see a third person just casually sucking one of their blood from the neck, yea it just pisses you off. Its a human thing. This isn't a human story.
Oh and another thing is that our main character isn't there to date her. Look, no matter how much a couple is shipped it all comes down to the characters. He isn't a cool looking guy, or someone with friends, he is really trying to be part of his class community but is scared of it, his first friend is a girl, yea. Doesn't have to mean they should be dating. I know in the one page he stops the whole thing, but then he prostrates because he knows its wrong to do something the genjin think its normal, similar to pushing his beliefs onto others, something he isn't the type or capable of doing. You guys have to understand the character, not push him into a harem.
Anyways, I like NTR so.....