Love.

Love is as necessary for your mind and body as oxygen, it's not negotiable. The more connected you are to love, the healthier you will be both physically and emotionally. The less connected you are, the more you are at risk.
It is also true that the less love you have, the more depressed you are likely to be. Love is probably the best antidepressant there is due to the fact that one of the most common sources of depression is feeling unloved. Most depressed people do not love themselves and they do not feel love by others. They are quite self focused, thereby making themselves less attractive to others and depriving themselves of the opportunity to learn the skills of love.
There is a believe that love just happens. This believe often makes the depressed sit around, passively waiting for someone to love them. However, love doesn't work that way. To get and keep love,you have to go out and be active.