Okay, so there are several novels and series with the title 'Dirty Diaries' floating around, mostly in the erotica/romance space, and the plot really depends on which one you're talking about. The one I'm familiar with is a dark mafia romance by K.D. Robichaux. It follows Sloane, a woman who's basically living a double life—by day she's a prim and proper preschool teacher, but at night she runs an anonymous, ultra-popular erotic blog called the 'Dirty Diaries' where she writes about her secret, wild sexual fantasies.
The main plot kicks off when her dangerous, obsessive fan, who happens to be a powerful mafia boss, tracks her down. He's been reading her blog religiously and becomes obsessed with making her his. It becomes this intense game of cat and mouse, blending suspense with super steamy scenes. The core tension is all about secrets, identity, and what happens when your deepest, most private fantasies are discovered by someone who can—and will—use that knowledge to own you completely. Ends up being a pretty wild ride.