Well it starts off as a purely practical point of changing rooms as Harriet wished they hadn't slept in Noakes' bed. He's trying to do what she wants again, but the way he puts it leaves her not sure what he means either and they end up in a downward spiral of "maybe he/she doesn't want to". The moment of negotiating the first night they *don't* have sex has to happen at some point in the relationship but night two of the honeymoon is probably a bit early. It would have been even more reassuring if Harriet had dragged him *in*, convincing him that he might possibly be capable of taking her mind off the spectre of Noakes in his nightshirt.