OP here.
many people would say that staying with an abusive spouse is insanity. If the wife has an ex boyfriend who promises to cherish her and respect her unlike the present husband why should they be like that? How does society benefit with people being unhappily married?
It is not required to stay with an abusive spouse. However, saying that people can can divorce and remarry whenever they are not happy led to the current situation of a 50% divorce rate. This situation means that millions of children suffer the pain of growing up in a broken family. Millions of children are facing the increase risk of problems associated with being fatherless - crime, drug abuse, teen pregnancy, etc.
Society benefits when divorce is not allowed because it means that there are more stable homes for children to grow up in. It does far less harm to a child to have unhappy parents than to have divorced parents. Divorce is devastating to children. Strong families are the basis good spiritual and emotional development. That is what is lost when people make a god of "being happy" rather than follow the commands of the true God.
It does not matter if this particular couple does not have children. Every divorce is an attack on marriage. Every attempt to justify divorce is an attack on marriage. And marriage is for creating a nurturing environment for children. When you destroy marriage, you destroy children and when you destroy children, you destroy society.