We've gone from being group animals to being recluses. Apes were never vastly gregarious to begin with. It is not loneliness thus, that is the problem, it is the realization and the acknowledgement of it to ourselves that is. There is no cure. There's just going on and getting used to it.
The cases worsen with over thinking, over analysis and over mourning of the fact that friends, family and the like are really no help, that they are trapped in cases of their own making and to them, you are not much help either.
The suggested remedy is to simply stop expecting. And then to find something to do.
In cases of severe depression that loneliness brings, making shallow cuts on one's peripheral limbs eases the numbness. As do some drugs that elevate hormone levels in the brain to create a general sensation of percieved well-being and an elevated sense of glee at mundane events such as the rising of the sun, floral arrangements, the apparent and exhibited joys of other people, etc.