If you thought that a marriage could succeed on love alone, please rethink. Love is transitory. The mutual attraction or the infatuation that comes in the initial phase of love disappears soon. After that what is left is the feeling that he/she is mine and I am his/hers. We have to journey together.
How a marriage changes in character after love disappears? This can occur in many ways. For example, the couple may begin regretting the marriage after the finishing of initial love phase. Or the couple may continue together as a sense of duty with each other and begin making a life together without passionate love. That needs caring for each other.
If you look back and think of marriages few decades back, most of the couples cared for each other. They called it love. It was essentially caring. A mother cares for her children because they are her responsibility and they belong to her. Similarly, partners care for each other because they got married. This kind of thought process can take the marriage last forever. The different thought processes of I want my freedom. I made a mistake. I am not happy with you. I must search for somebody better and so on leads to...