The Haunting of Gabriel Ashe

So far, the best thing about The Haunting of Gabriel Ashe is the basic idea behind the novel.  I say this meaning that it is fast-paced, interesting, and incorporates an idea of demons that has been in humanity forever, but in the story is presented in a fresh way.
In the novel, the name of the demon is The Hunter.  Gabe and his friend Mazzy, and his neighbor Seth, can't be sure in the point of the book where I am if The Hunter is real.  Seth is a firm believer.  The Hunter originated in a game between him and his older brother David.  David ran away, convinced that The Hunter was real and after him, and Seth missed the game so much that when Gabe moved in the summer before eighth grade Seth could hardly wait to play it again.
When school starts, Gabe makes new friends and they help him to be convinced that Seth is a freak, and not someone Gabe should be hanging around.  Several strange occurrences happen at school that Seth is seemingly behind, but only Gabe and Mazzy believe Seth when he pleads innocence, while the rest of the school only wants to make him even more of an outcast.
Something else must be behind everything, something greater than Seth.
I believe that The Hunter is real, but instead of a moster that has always existed, I believe it is something accidentally conjured up by Seth, Gabe, and Mazzy.  All three of them came from rough times in their lives, and all three try to convince themselves that they are fine when they really are not.  Before David ran away, other things were happening in his life he couldn't deal with, such as people making fun of him at school.  The Hunter didn't start bothering him until these prior things occurred.
So, what do you think will happen next?  Is The Hunter a demon that's always been there?  Is there even a demon at all?  Or is it just a product of their minds?