On p. 252 Nathan says: "Juliette never let go of the why, which seemed to bother her more than the actuality. She searched for a reason that would put his infidelity into a paradigm she could understand and thus prevent from happening ever again. As though if he revealed the truth, she'd then understand how to prevent him from straying."
Do you think that understanding why something happened is necessary to fully forgive what actually happened?