Your mother's "just let things go" deal is how she tries to live with the trauma in her own life...and I would guess she has had plenty or she would not have said "learned years ago". It is not unreasonable for you to want her to show compassion over what happened to you, but she is either unwilling or unable to risk the loss of her own sense of security (her marriage) by doing so. Your father is a sick man and your mother knows that, but she lacks your motivation and courage to hold him accountable.