In the movie "Candy" with Heath Ledger, what happens at the end?

What happens in the end? I know he tells her it's better off how they were, but he looked sick and I was left wondering if he had aids? Or was sick in some way? Or was he still using? I was under the impression that he had stopped using after Casper died. But at the end, his eyes(well rather, one eye) was red and slightly puffy and he acted a bit anxious. Does anybody know? Does the book say? I never read the book. But I would like to know. I'd appreciate the answer, thanks.