The world has become a place where people from very different parts of the world and cultures can meet on a regular basis, but different traditions can effectively make a permanent relationship between two people impossible. One person might have grown up with the idea of choosing their own spouse, and their potential partner might believe they should marry the person their family has chosen. Each of them might be in love with the other, but their ability to be together can be compromised by their family traditions.
There are other issues that can keep two people apart, and families have often cited religious or cultural differences to keep young people in love from marrying. They could find they do not even celebrate their holy day on the same day of the week, or one of them could feel a deep religious connection when the other has none. These issues will need to be resolved in some fashion before the two of them choose to plunge into a long term relationship.