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. 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.