
"A primordial area of the brain creates both the capacity and the need for emotional intimacy that all humans share. A General Theory of Love describes the workings of this ancient, pivotal urge and reveals that our nervous systems are not self-contained. Instead, our brains link with those of the people close to us, in a silent rhythm that makes up the very life force of the body. These wordless and powerful ties determine our moods, stabilize and maintain our health and well-being, and change the structure of our brains.". "A General Theory of Love applies these and other insights to some of the issues we face in our lives. Its authors explain how relationships function and where love goes wrong, how parents shape a child's developing self, how psychotherapy really works, what curbs and what fosters violent aggression in our children, and how modern society regularly courts disaster by flouting emotional laws it does not yet recognize."--BOOK JACKET.
Attached https://www.amazon.com/Attached-Science-Adult-Attachment-You...
A General Theory of Love https://www.amazon.com/General-Theory-Love-Thomas-Lewis/dp/0...
Attachment Disturbances in Adults: Treatment for Comprehensive Repair [academic/professional text] https://www.amazon.com/Attachment-Disturbances-Adults-Treatm...
2) It's harder to make friends as you get older. Most friendships are built on an ongoing shared experience that is challenging, such as being in school together. Most of my adult-onset friendships are a result of having worked in small startup companies that were struggling to survive. Casual meetings of potential friends are much less likely to generate the energy and commitment for developing a friendship. If you're interested in the research on this, look into the work of Robin Dunbar, e.g.,
Friends: Understanding the Power of our Most Important Relationships https://www.amazon.com/Friends-Robin-Dunbar/dp/1408711737/
I used to have a museum membership so I could go everyday for free if I wanted to. I often went every other day just to get coffee, or to use the free wifi for work. It was subjectively a very different experience than being with someone.
I am pretty sure if you measured something like endorphins or blood pressure, you'd see there was more enjoyment with someone than without. There are tons of studies that already do this, e.g. the ones written up by UCSF profs in "A General Theory of Love."