Relationships are an important part of life but it isn’t clear that economics involves relationships until one starts reading anthropology. As anthropology sometimes deals with small societies in which there is no money it is much clearer that relationships are very much a part of the exchange of goods and services.
Where there is no money generally people have to work together or make exchanges via gifts. In both situations ones relationship to others is a part of the cooperation or the exchange. In some cases what appears to be items of little apparent use or value are exchanged in order to define a friendship.
The use of money allows exchanges with many more people most of whom are strangers. Even so we can consider there to be an economic relationship in these exchanges.
It might be possible to analyze economic history and economic development in terms of how relationships have changed or are changing. Clearly relationships in a feudal society were different from those in our own times and probably relationships during early industrialization were different still.
It may be that our relationships are more complex than in earlier times. We now have relationships, with the people who produce the goods and services we consume, the people we work with, the people we sell to, our neighbors, people with common interests and people who represent government.
In my experience one of the most important things about relationships is that to have a satisfactory relationship there must be an equal exchange between the people involved.. Unfortunately not all relationships are satisfactory.
Studying relationships as a part of economics may not help predict future GNP but it might encourage us to make our economy more rewarding and satisfactory.