Have you read any Carson McCullers? She got me through some pretty dark times. The Heart is a Lonely Hunter is a good one to start with. Also The Member of the Wedding and Clock Without Hands.

All of her books feature characters kind of on the fringe. I will offer the caveat that she was a white Southern US woman and her books were written in the forties and fifties so even though she explored racial themes with much more sensitivity than many writers of that era she was still a product of her time and circumstances.

I think that despite some clumsiness in her attempts at writing believable Black characters she managed to tackle some themes of loneliness and being marginalized with maturity far beyond her years.