A relationship journal is a type of journal that, instead of being used by one single person, is used by two or more people. The intention behind using a relationship journal is usually to mend and/or strengthen a relationship that might otherwise need it. Seeing as every relationship is different to greater or lesser degrees, it stands to reason that each relationship journal should be different. In this way, you really can fill it with anything you like, even if it does not directly better the relationship. Indeed, it is yours to customize as you see fit, so long as your lover in crime agrees too.