[I started this post in 2007 and never finished it, though I thought I had. I've tweaked the beginning and gone on from there.]
Some years ago, I discovered a writer for teens/young adults named Caroline Cooney. One of her better-known books, which my daughter picked up at a book sale, is The Face on the Milk Carton, about a girl who discovers she was abducted as a toddler and as a consequence, has to reexamine and reinterpret her life. I liked it enough to read the three sequels.
In that series, and even more explicitly in some of her other books, Cooney unflinchingly faces the terrifying fact that our actions can have irrevocable consequences. The only other author I can recall reading who does the same is George Eliot, the 19th century novelist most famous for Middlemarch. The novel featuring this theme most directly, however, is Adam Bede.
If you've read the work of either author, you might want to check out the other.