The other “wrong” reason to enter into a relationship is, like Greg said, to “fix” yourself. This desire to use the love of someone else to soothe your own emotional problems inevitably leads to codependence
Many people never learn how to breach this deep, unconditional love. Many people are instead addicted to the ups and downs of romantic love. They are in it for the feels, so to speak. And when the feels run out, so do they.
Amazingly, these couples survived because their respect for each other allowed them to adapt and allow each person to continue to flourish and grow.