Falling in love with someone and having a relationship are two different things. The day-to-day goes on for a very long time and creating a relationships that lasts is about resolving issues that will make a relationship end. The trick with relationships is not making relationships last; it’s keeping relationships from ending. 

All relationships end for the same reason: problems of a relationship are greater than the desire, or the skill, of people in the relationship to solve.

—  Infpblog.com