I read this short book about 30 years ago. As I recall, it is about an astronaut who lands onto earth in the future. Society is focused on being in harmony with nature, and has moved away from advanced technology, particularly nuclear technology. They have an awesome recycling capability. Society has given up on strict monogamy, and whenever someone wants to take a lover, they're allowed, and it's considered a breach of etiquette to get jealous or complain. One of the central issues is deciding what to do with his rocket ship -- as I remember, they want to dismantle it, so it can't be turned into a weapon. Any help with this is greatly appreciated. 
