YA Boarding School/ College. Unreliable narrator. Classmate is a vampire? Possible Read early 2000s. Spoilers.

[AquaMoon]

Told in first-person, possibly journal format. Narrator is attending boarding school or college and becomes convinced her classmate is a vampire who is stalking her best friend. Narrator becomes increasingly obsessive about this idea. I don't recall if the vampire accusation is proven or if the accused classmate is just really strange. But I believe the best friend falls ill and dies toward the end of the book.

I read this one back in the early 2000s and can't for anything recall the title, but I feel it was completely irrelevant to what the book was about (which is probably why I can't recall it). In any case, I'd like to revisit it.

Thank you :)

[Becca]

The Moth Diaries by Rachel Klein?