To believe being alone is unbearable, the person must be deluded about being alone. If it is unbearable, then it must the fear of suffering in isolation which leads one to the false beliefs we have about loneliness.

Being alone is solitude. When one examines his mood in a crowd, finding himself alone there, then he believes being in a crowd is unbearable.

In actual fact, it is his disconnection from the community which causes loneliness to manifest in a disagreeable manner.

Because the natural reaction to loneliness is to retreat from it mentally, one finds it to be unbearable.

The cure is simple: pick one person to talk to about what they wish to talk about, and with practice, when you bond with people, all loneliness will be forgotten.