I thought they meant The Alchemist by Paulo Coelho. I read some of his books as a teenager. Looking back they felt weird. I think I just thought everything was deep back then.

Looking back The Zahir definitely felt like cuckold smut though. The main character's wife leaves him for another man and he has to go on a spiritual journey to find her. The spiritual guide is the man she left him for. At some point he talks about having fantasized about his wife with other men. In the end when they are reunited she is pregnant. Just a very odd book looking back.