“… romantic love did not evolve to help us maintain a stable, enduring partnership. It evolved for different purposes: to drive ancestral men and women to prefer, choose, and pursue specific mating partners, then start the mating process and remain sexually faithful to ‘him’ or ‘her’ long enough to conceive a child. After the child is born, however, parents need a new set of chemicals and brain networks to rear their infant as a team — the chemistry of attachment. As a result, feelings of attachment often dampen the ecstasy of romance, replacing it with a deep sense of union with a mate.”

Helen Fisher, Why we Love, the Nature and Chemistry of Romantic Love P. 92