Izgad recommended a while back that I read Joseph Soloveitchik’s Lonely Man of Faith. To be honest, I’ve had a hard time getting into the book, plus I’m not entirely sure why the “man of faith” is lonely. But the following passage on page 36 offers a good description of loneliness:
He struggles for the discovery of his identity because he suffers from the insecurity implied in seeing the icy darkness of uniformity and irresponsiveness, in gazing into that senseless something without being awarded a reciprocal gaze, in being always a silent watcher without in turn being watched.