Guinea pigs are prone to loneliness --- In Switzerland, it is illegal to own only one.
Loneliness is anguish not because one has no one to share one's burden, but rather, because one has only one's own burden to bear.
Loneliness is a gift that sometimes enables a radical vision of society or one's people that has not previously been taken into account.

However lonely you feel, you're never aloneThere are literally millions of bugs, mites and bacteria living in your house. Goodnight
Loneliness is marked by the horror of color, the roar of soundlessness and the menace of familiar objects lying still.

Loneliness is a naked terror which few know, as even the most miserable outcast hugs some memory or some illusion.
Loneliness is a need that is not satisfied if one sits at a table alone. There must be empty chairs as well.