In Harvest Moon, there usually is a sequence of Events known as 'Heart Events' that are the foundation of your character's courtship of any Eligible Girl or Eligible Bachelor.
In Rune Factory Frontier, each Eligible Girl has her own 'Story' and there is a still that is included in the 'Memories' section of the game only when her Story is completed. Although the Events in an Eligible Girl's Story have been called 'Heart Events', strictly speaking, they are different, as you evidently CAN experience them after marriage. True 'Heart Events' cannot be experience once you marry.
In fact, one player actually took another Girl out on a Date in Rune Factory Frontier AFTER marriage to Mist!
I always experience all possible Events BEFORE I save a Marriage to any Eligible Girl or Bachelor either in Harvest Moon or Rune Factory. I therefore had completed all the Stories in Rune Factory Frontier while remaining single. I should not have made an assumption to the effect that these Stories could be equated to Heart Events in every respect.
In any case, my Guides will be revised to include the information that the Stories of other Eligible Girls can be completed after you marry some one else. What you cannot do is marry an Eligible Girl if you have not completed HER Story yet.