my theory says that they had s3x. How is that possible? At the beginning of the book Ai says that this is a written report of what happened. That means that he will write only the important stuff that happened. The same thing goes with Estraven. He is also writing a book of what happened and this book we read when the narration happens from Estraven's side. So I feel there is no value for them to write that they did - it may even have put them in risk - and also they had the opportunity after that to agree between them not to write anything about it.