" John Bowlby understood that our need for someone to share our lives with is part of
our genetic makeup and has nothing to do with how much we love ourselves or how fulfilled we feel on our own. He discovered that once we choose someone special, powerful and often uncontrollable forces
come into play.

New patterns of behavior kick in regardless of how independent we are and despite our conscious wills.

Once we choose a partner, there is no question about whether dependency exists or not. It always does. An elegant coexistence that does not include uncomfortable feelings of vulnerability and fear of loss sounds good but is not our biology. What proved through evolution to have a strong survival advantage is a human couple becoming one physiological unit, which means that if she’s reacting, then I’m reacting, or if he’s upset, that also makes me unsettled. He or she is part of me, and I will do anything to save him or her; having such a vested interest in the well-being of another person translates into a very important survival advantage for both parties. "

― Amir Levine , Attached: The New Science of Adult Attachment and How It Can Help You Find—and Keep—Love