The Once and Future King Book 3, Chapter 14
Arthur asks Lancelot to stay at the castle while he helps another king at war. Lancelot and Guenever are thus alone together for a year, during which they are completely happy. Lancelot feels some remorse, though Guenever does not. He tries to tell Guenever his secret about how he hated (and still hates) himself, and has always wanted to do miracles, and how now that they have sinned, he can never do it again. She misunderstands and thinks he would rather be holy than be with her, when really what he means is that he has traded his holiness for life with her.