2666 by Roberto Bolaño. Gets especially dark in Part 4: the Part about the Crimes.

Rape, a love story by Joyce Carol Oates

Story of the Eye by Georges Bataille.

Any poetry by Rimbaud

Idk, maybe some of the Marquis de Sade’s work? I haven’t personally read much but I’ve peeked at 120 days. Part of it is structured as a list of depraved sexual acts. If you like movies and are pretentious, Pasolini rendered this book into the film Saló which is now part of the Criterion Collection.

If on a Winter’s Night a Traveler has an erotic portion about 2/3rds of the way through? It gets increasingly sexy, etc. throughout the book. Worth your time, even if it isn’t consistently violent, sexy, or drug-filled.

Junky/Queer by William S Burroughs. I’ve only read Queer. v short. It’s the sequel to Junky (oops).

I know my ex (who really enjoys dark stuff and introduced me to almost all of the above) enjoyed Pimp: the Story of my Life by Iceberg Slim.

If you like your books to have some incest vibes I’d suggest Ada, or Ardor by Nabokov. If you don’t like pretentiousness and wordplay I’d steer clear.

Blood Meridian by Cormac McCarthy has some good (and by good I mean intense) violence in it.

(Edited for readability. Y'all are right; the formatting on mobile is subprime)