The concept of romantic love is an outgrowth of the Middle Ages tradition of chivalry, a set of ideas and customs associated with knighthood.
The knight was expected to pay courtly love to a noblewoman. This involved writing poems and jousting in tournaments with the fair lady’s handkerchief tied to a lance. The lady was often unattainable, and sexual desire was unrequited. The present-day concept of courting a woman is obviously derived from the days when knighthood was in flower.
It is only in relatively recent centuries, and primarily in the Western world, that the concept of romantic love has been tied to actual marriage. The problem is that romantic love has a certain tendency to fade after a marriage settles down and children become members of the family. True, there may be romantic moments, but one cannot expect a steady state of limerence to endure day after day for years Read What is Love and Intimacy
Romantic love is replaced with conjugal love, a state of deep affection, mutual respect, and shared responsibilities. The partner is loved and there is intimacy. And it is necessary to be more or less satisfied with conjugal love if one is to have a stable marriage. If there is a demand for romantic love, then this may play a role in a desire to have an affair or seek a divorce.