Books on mundane loneliness

I'm going through a transitory, isolated-feeling stage in life, and I'm finding a lot of comfort in books.

I lean towards fiction, but non-fiction is fine. I prefer no fantasy. I'd like something pretty much grounded in reality. Something touching on the human feelings of disconnection from both society and interpersonal relationships, loneliness, general expansive themes. Simple in plot, but confronting complex emotion.

Recently, I read and LOVED Stoner by John Williams – the best description I've found for it is, "a book on how everyone lives a life, whether it's remembered or not."

Thanks in advance!