The Darkness complete book

A story about a young man who finds himself in a mysterious underworld of fantasy and horror. Falling in love with a beautiful girl and trying to come to terms with what is happening to him, is it in his head or not? There is a whole history of this fantasy world that he discovers. Story of friendships and loved ones, going down a rabbit hole to find true love or so he thinks. The story starts with a mysterious Professor and a ‘voice of reason’ detective.
Hopefully, the story takes the reader on a journey from normal to insane.