Staying on top of a career and social life consumes many hours daily in the modern world, and being in a relationship doubles the duties. When a person has a partner, they must consider their partner's schedule as well as their own. Twice as much frustration can result from this need, and it can break a relationship into pieces when two people have incompatible schedules. Continually making excuses for a busy partner does not help the situation, so there is little wonder that a couple may decide to end their relationship.
There are couples with opposing schedules who will work out their differences, and they manage to keep their relationship healthy throughout the years. They long ago accepted the truth that life is often hard, and they are willing to make sacrifices for each other. Unfortunately, many younger couples simply see this as a reason to end their association and move on to be with someone more amenable to their schedule.