Plot points/FAQ **SPOILERS**

To answer some of the questions raised in this board based on having read the book AND watched the movie. This is MY interpretation only and the book does get a bit ambiguous toward the end. Please feel free to add any additional questions and/or to disagree with my take on what happened.

1) What exactly does Nathan do in the truck that freaks Roy out?
While it's NOT clear in the movie, Nathan initiates anal intercourse with Roy by straddling him. Since Nathan has promised Roy that he's never done anything with anyone else, the ease with which Nathan does this enrages Roy.

2) Does Nathan Die? If so what happens after?
Nathan dies in the plantation house and the police and his father come for the body. Nathan's spirit "comes to" in the house after that and wanders back into town in time to see Roy coming from the funeral. Roy can see Nathan's ghost. Both the book and the movie end on an up-note of sorts... it's suggested in both that Roy and Nathan's relationship has survived Nathan's death. And Nathan seems happier in the end.

3) Is Nathan dead from the beginning of the movie?
No, he was just showing the effects of his dad's sexual abuse. In some ways, the ghost Nathan we see at the end looked more lively than the living Nathan looked at the beginning of the film.