Short answers, pulled from the story.
In social psychology, an interpersonal relationship describes a social association, connection, or affiliation between two or more people. Relationships vary in degrees of intimacy, self-disclosure, duration, reciprocity, and power distribution, and they form the basis of social groups and societies.
Ellen Berscheid and Elaine Hatfield are credited with establishing relationship science as a rigorous, evidence-based field through their research during the 1990s. Their work helped consolidate findings from anthropology, linguistics, economics, and other disciplines into an interdisciplinary science.
George Levinger proposed five stages: acquaintance, buildup, continuation, deterioration, and ending. He originally designed the model for heterosexual adult romantic relationships, but it has been applied to other types of interpersonal relations as well.
Harry Harlow's 1958 study showed that infant rhesus monkeys sought affection from cloth surrogate mothers rather than just the wire surrogates that provided food, disproving the idea that infant love was purely a biological drive for survival and comfort. The study laid the groundwork for Mary Ainsworth's attachment theory.
Individuals in long-distance relationships rated their relationships as more satisfying than those in proximal relationships. Long-distance couples reported lower costs and higher rewards compared to couples who lived near each other, and LDR couples saw each other on average once every 23 days yet reported similar satisfaction levels.
60% of people report being friends with one or more former partners. Separately, 60% have experienced an on-and-off relationship, and 37% of cohabiting couples have broken up and reconciled with the same partner.