The story of Goddess Lakshmi, Ganga and Saraswati as wives of Lord Vishnu is mentioned in the Brahmavaivarta Purana and Devi Bhagavatam. There was no unity among the three wives. Arguments and quarrels were a constant feature.
Once, a major quarrel broke out between Goddess Saraswati and Goddess Ganga. Both were feisty and temperamental. Goddess Lakshmi attempted to make peace between the two but she was ignored.
The fight took a real ugly turn and the two cursed each other to become rivers on earth and absorb sins of the people who bathed in them.
Lord Vishnu failed to control his two tempestuous wives. He abandoned the two and decided to have only Lakshmi as his wife. Later, Brahma gave refuge to Saraswati and Shiva gave refuge to Ganga.
Such stories in Puranas are a warning to human beings who engage in multiple relationships. The story symbolically states that even Gods cannot be happy with multiple wives or husbands.