This is an interesting article in the Washington Post about a study of loneliness by Christakis and Cacioppo that purports to show that loneliness can be spread from person to person. They theorize that a lonely person interacts with others in negative ways due to their emotions and that affects those they interact with. Lonely people tend to become isolated and loneliness increases. The particularly mention loss of a spouse or a divorce as being a trigger for loneliness and say that loneliness has far-reaching consequences for mental and physical health, bringing with it depression, sleep problems and ill health.
I certainly saw the consequences of loneliness in Leif, and he did become increasingly isolated, except for a very small group of acquaintances. He perked up and seemed a lot happier in a big family grouping, but rarely had that opportunity. He tried hard to find someone to love but did little to cultivate any other kinds of new friendships.
His physical health suffered; his asthma was worse; he gained weight, had insomnia. Feeling worn out and having trouble breathing would feel awful and make it hard to function or be happy and sociable.
It's sad that the breakdown of relationships, even those that are destructive and unhealthy, can cut someone off from the kind of intimate human contact that can prevent loneliness and all that goes with it.
This reminds me of the studies we learned about in psychology of infants who fail to thrive, eat and grow properly because of a lack of touch and human stimulation. I think something similar happens in adults who lack loving touch and human contact and warmth. Something just shrivels up and dies in them.