I can tell you one way they began––
They met when they were children, stayed together through high school, and married a month after graduation. They went to college, got internships in different states, successfully managed a long distance relationship for a year before finding a home and jobs to raise a family. They’re there now, in their two story house, struggling to pay the bills and arguing with their children over their behavior or their homework.
––or I can tell you another way.
One fell ill due to some terminal sickness of your choosing (tumor, cancer, etc.). The other became a successful actor(ess) and fell into bed with numerous people in their world. The famous one got into an accident, went to the same hospital where the other was receiving the news that they had very little time left. They met in the cafeteria. They dated and they fell in love. The sick one died and the famous one occupied an idle life.
Maybe I can tell you the truth.
They’re enemies at first. Think of all those star-crossed lovers you’ve read in fiction that you know should be together but aren’t because of families, morals, etc. Some force brings them close, teaming them up time and time again. Secrets stop them from acting on their feelings. They’re friends here, married or occupied with others, sneaking off to have adventures together but they’re not together.
What makes you think they aren’t happy though?
Listening to: Architecture in Helsinki––Maybe You Can Owe Me