Love, etc, by Julian Barnes

In Julian Barnes's 1991 novel, "Talking It Over", a love triangle appears to resolve itself when Gillian divorces Stuart and marries his former best friend, Oliver. A decade on, they reintroduce themselves to the reader and shatter any illusion that a marriage at the end of a story signifies happily ever after. Once again, Barnes allows his characters a conspiratorial, direct address to the reader – a technique that's so perfectly suited to the material and that makes the book so fun to read, I can only assume it's not attempted more often simply because it's too hard to pull off with such flair. Barnes proves that, as long as you maintain a certain disrespect for your characters, sequels can both improve, and improve on, the original.