Books where a happy main character has a complete 180 and they become insane or miserable?

I don’t really care how graphic it is, I am looking for a book where the main character starts off as happy, positive, etc, and then goes through a shitty, miserable life, so throughout the story they slowly lose hope in humanity, become depressed, miserable or negative, etc. Sorta like a downward spiral except the main character starts off as happy.