It's been awhile since I read the book but I agree about it being a really sad story. Arnie being betrayed by Dennis and Leigh. Arnie fighting for control at the very end before the wreck with his mother. Dennis and Leigh not being able to stay together because of the memories of what happened.

Yes to all the things you mentioned, especially the part about Arnie fighting for control at the end. I went into the book expecting Arnie to die, but became a little hopeful closer to the end, thinking he may become strong enough to overpower Lebay. It was pretty sad.

I find that a lot of King's books have more sad moments that actual scary moments
I know. That's why I keep jumping into his stories. I know that I am always guaranteed all these layers and story with his books. To be honest, I don't even think there are that many King books that I classify as horror. They're so much more than that.