WhiteTim said:
I'd rather it be set in America, but a bigger problem is that it was first published in 1942.
Lol... you seem rather picky here to have a problem over a matter of a few years. In all seriousness
The Stranger would seem to come closest to what you are looking for, unless you can give us some more to go on. You may want to check it out regardless. Camus is a philosopher and the book is meant to be somewhat timeless. Another book I have not read but am told is somewhat similar is
Nausea by Sarte.
There is
VALIS by Philip K Dick.
This one is a rather strange sort of autobiography. It would seem to be the life story of a mad man through the eyes of the mad man. Dick was married and divorced. He had many strange experiences which he was never quite able to reconcile as madness or reality. He attempted suicide and was placed in institutions multiple times, every time being released with a clean bill of mental health.
Devine Invasion and
Radio Free Albemuth are both fictionalised variations on
VALIS but less likely to fulfill your criterion.
Many of Dicks books revolve around characters who are single, divorced, or who have rocky marriages. Arcter in
A Scanner Darkly is single though he has roommates. The book is quite good. While the movie is actually pretty damn close to the book the book is much better.
In
Last Call by Tim Powers the main character is divorced and living alone though the story line takes him out of this situation and on the road with his best friend and the father he hasn't seen in years. Its a fantasy novel revolving around poker and mysticism.
Astronuc mentions
On the Road which is another great book. The character is primarily single through out, though not always, and lives alone mostly but keeps moving from place to place. I'm actually thinking of rereading it now, its been about a decade since I read it.
The main characters in Koontz novels often seem to be single and living alone (sort of) though there are almost always love interests.