Whether we should stay in or leave a relationship is one of the most consequential and painful decisions we are ever likely to confront: few other issues will have such power to trouble us. What makes the issue so hard is that there are no fixed rules for judgement. How can we tell whether a relationship is ‘good enough’ or plain wrong? How do we draw the line between justified longing and naivety? Is sex vital or could it be foregone? Does someone ‘better’ actually exist? How much should the feelings of children be counted (and what might they be in the long term)? Could one’s partner change, perhaps with therapy, or should one assume that who they are now is who they will always be?