Did the stuff described in "120 days of Sodom" actually happen?

Reflecting on recent events, I've been wondering if aristocrats have always engaged in immoral sexual activities in secret, and then I remembred: 120 days of Sodom

I started reading that book years ago, but it was so disturbing I couldn't finish it, and yet what it describes sounds a lot like the things we now know to be commonplace among current aristocrats

But then, I wonder, is the stuff described in 120 days of Sodom real? Maybe those four specific nobles were fictional, but was the stuff they do in the book inspired or informed by real events?