The meaning of the title tenth circle?

Answer 1

In the book, the wife teaches a college course over Dante's Inferno, which involves his definitions of the nine circles of hell. Near the end of the book, Laura (the wife) asks her class if he managed to cover every sin a person could cover. To herself, she answers it with what she defines as the tenth circle of hell,

"He wrote about sinners and the nine circles of hell. And I realized there should be another one. One reserved for those of us who have lied to ourselves by pretending we aren't hurting the ones we love. The tenth circle." - From the movie

Throughout the story, each of the main characters act in such a way that they don't realize how their actions affect the ones they love until it was too late, which is how Laura comes to this conclusion