He broke his neck when diving into shallow water, and he wishes he'd died then, that someone hadn't pulled him up at the last minute. Even though he can't see the beach from his bedroom window, many of his ideas and remembrances encompass the water.
There's a bit where a quad priest comes and yells back and forth up and down the stairs about God owning life, which brings again the point that quads can have valuable lives. In fact, our protagonist turns out to be very good at designing equipment that his nephew and father make. But no matter how happy he is at any point, he still wants to die. He has a chain of friends worked out, where each friend does one small, legal in itself, part, but he's looking for someone who will do the final step.
It's a hard movie to watch, but a really good one.