The Mysteries of Pittsburgh by Michael Chabon (1988)Read about another entry on the list.
The now established author of Kavalier & Clay began his career with this rewriting of The Great Gatsby, set in 1980s Pennsylvania. Protagonist Art Bechstein questions his sexual orientation, and his alienation heightens his sensitivity to the world around him. In one of the novel’s final scenes, Art studies his ex-girlfriend with a kind of affection and understanding that comes to feel like revelation. “I was impelled now to look more closely,” Art says, pinpointing the chief virtue and gift of solitude, “to try to see the whole and its parts at the same time … the fine join of earlobe and jaw, the bone beneath her eye, and as I looked, it was no longer a profile.”
Also see Teju Cole's top ten novels of solitude and Robert Williams's top ten loners in fiction.