Human relationships are shown in a superficial way with no attempt to go to the root cause on why relationships between 2 individuals is the way it is .Yes. That's a fact. We do not want to accept it because it destroys the myth that human relationships are something marvelous or extraordinary. We are not honest, decorous and decent enough to admit that all relationships are built on the foundation of "What do I get out of this relationship?". It is nothing but mutual gratification. If that is absent, no relationship is possible. You keep the relationship going for social reasons, or for reasons of children, property, and security. All this is part and parcel of the relationship business. But when it fails and does not give us what we really want, we superimpose on it what we call "love". So, it is just not possible to have any relationship on any basis except on the level of mutual gratification.
The whole culture has created, for its own reasons, this situation for us through its value system. The value system demands that relationships be based on love. But the most important element is security and then possessiveness. You want to possess the other individual. When your hold on the other becomes weaker for various reasons, your relationship wears out. You cannot maintain this "lovey-dovey" relationship all the time.