It is certainly difficult for him to accept his wife was raped in front of him and he couldnt do anything to save or help her. As much as he might not be able to forgive himself,it's possible he feels he can't protect her,yet it's not a enough reason to walk away. Every rape victim needs to be loved and cared for,not rejected. His rejection of her might cause more harm to her. They both need to heal and can get through it fast together. Sticking together at this time would make them stronger. She needs him now more than before.
