Your species developed in small pack-like social groupings. As such, your species relies heavily on intimacy - touch, hugs, cuddling, and socializing.
When I worked with the sick and dying, one of the most common features of their later days was that friends and relatives would pull back and stop giving them touch - their health would immediately start declining faster. Why the pulling back? Because during this sorts of situations people start breaking the connection that they know death will bring.
There is a lot to say about cuddling and hugging:
http://www.lifehack.org/articles/lifesty...e-now.html Is a good start.
I recently read in one of the psychological journals in a doctor's waiting room that depression can be caused by lack of touching, and that those with depression can get near instant relief from casual cuddling, with even a potential to be 'cured' from depression once they start getting regular cuddle/hug times.
Which may explain why depressed single people continually believe that the right partner will make them happy.
The biological chemical processes are most fascinating - sadly modern society doesn't teach these sorts of things via public education to make it clear that humans are social creatures who need human contact.
In other related areas, An experiment was done with a colony of rats who had a happy enough place. They had two water bottles - one was spiked with heroine, the other was just water. Only the rats who were isolated kept going back to the drug laced bottle.
This experiment was done because an earlier experiment isolated rats and gave them two bottles - in that experiment a huge percentage (80%+) became habitual users of heroine laced water.
Rats, like humans, are social creatures - they are also prone to many of the same ailments that humans are prone to during stress.
Thus these experiments do teach us a lot about how human behavior is molded and sent on certain trajectories based on how much a person is touched, how solid their social circle is and other factors along these lines.