And I lose faith...
"I didn't get it until I read the novel but it's definitely a Renfield relationship." Uhh... No. That's only in the remake, Let me In. Reading the novel would tell you the relationship was very, very different, the boy is NOT destined to be Eli's new Henchman. The author hates that "interpretation." It's supposed to be a platonic and real love, that's why in the sequel short story the author had Eli make Oskar a vampire.
http://bloody-disgusting.com/news/3414545/let-right-one-pilot-like-draculas-seduction/