This story was a wonderful, disturbing exploration of insanity on the order of "Escape to Thin Mountain" (Pseudopod 547, discussion here:
http://forum.escapeartists.net/index.php?topic=10171.0).
I was especially impressed with the depiction of the protagonist's development from a rather ordinary little boy, consumed by a child's passion for something (he learns about fey the way other kids acquire an encyclopedic dinosaurs, or planes, or butterflies), into a sexual predator. The author does this without relying on explicit descriptions of sex, violence, and gore, which I think really increased the sense that the protagonist is experiencing an increasing separation from reality.