What are two questions left unanswered at the end of the book The End of the Affair, by Graham Greene?

The End of the Affair deals with a variety of spiritual and emotional topics and, as such, the ending leaves several questions without concrete answers. The nature of faith is one of the primary themes running throughout this story, and multiple loose ends are left after the narrative comes to a close. The two primary unanswered questions are whether Bendrix comes to truly believe in God and whether Sarah is a spirit who is capable of performing miracles or if this is merely the way her grieving loved ones have chosen to cope with her death.
Bendrix's Faith
At the beginning of the narrative, Bendrix is a staunch atheist. He and Sarah share a lack of belief until an air raid leaves him seriously injured at his front door. Rather than check to see if he is alive, Sarah retreats to his room to beg God to bring him back. She promises that if her lover's life is spared, she will end their affair in return. Bendrix lives and, unbeknownst to him, this is the real reason why Sarah stops seeing him. Only upon reading her diary many years later does Bendrix learn that she never stopped loving him. While he initially thinks that she has begun an affair with another man, he soon realizes that his greatest competition for her affection is the God whom she believes spared his life.
As the story progresses, Bendrix's apathy towards God turns to hate. After Sarah's death, his hatred unexpectedly takes a turn to openness. Sarah's own faith was born out of the epiphany that in order to truly hate someone, as Richard Smythe hates God, there must be some truth to them. Bendrix grudgingly comes to a similar realization and, towards the end of the book, he prays, "I'm too tired and old to learn to love. Leave me alone forever." Greene leaves it open-ended as to whether Bendrix will eventually adopt Sarah's reluctant faith in a God she once hated or remain in a state of grudging half-belief forever.
Sarah's Sainthood
After Sarah's death, there are reportedly several miracles that occur. Sarah's mother informs Bendrix that she secretly had a Catholic baptism as an infant. Her spirit is rumored to have the ability to perform miracles. After her death, Smythe's disfiguring birthmark disappears entirely. Parkis' son is also healed of severe internal pain with no apparent medical explanation. These miracles raise the question of whether Sarah has truly become a saint, despite the sins she committed during her life, or whether these instances of healing are mere coincidences.
These unanswered questions are part of the framework that makes this story so moving. By leaving some questions unanswered, Greene gives the story a surprisingly satisfying ending. It would be untrue to the thematic elements of the book and the characters themselves to answer either of these questions with objective certainty.