Looking for novels with strong themes of loneliness

Loneliness has been the main theme of my early 20s. It got so bad that there were points I couldn't bear to read books or watch things where loneliness was a big part of the story because, although validating, it would get a bit too painful.

As I find myself at the tail end of that chapter of my life (thank fucking god), I kind of want to test myself and see if I can get through a novel about being lonely.