Complex sentence: Ruth ends by saying she believes a person can repent as has Bob, but not everyone, as the final scene shows Ruth at a book signing for Mary's new novel--in which she tells all about her affair.
Split into simpler sentences: Ruth ends by saying she believes a person can change, as has Bob, but that not everyone does so. The final scene shows Ruth at a book signing for Mary's new novel--in which she tells all about her affair.