This manga is turning into an actual, diagnosable autism test.
She let the Vampire feed on her because, as a fellow non/ab-human, she literally thinks nothing of it and associates it with sharing food or literally donating blood. Meaning, our Vamp boy is on such a nonexistent level of romantic interest he's not even on the scale, he's not even friendzoned, he's fucking species-zoned.
While you might notice, when her nails are embarrassingly long, she's flustered to have that be pointed out by the MC, almost as if she cares about her appearance in front of him, which indicates?
If you can't intuit the answer to that question, and you can't understand how this concept is literally the opposite of NTR, you should know that the inability to place yourself in another person's shoes or understand social cues is an actual symptom of autism. You may have a rather severe case. That or you're just dumb, since the author basically spoonfeeds this to you.