CMP - what are you finding unbelievable, that a step-father could abuse his step-daughter? Because that would make you about the singularly most naive person in the world. There is a truly frightening statistic about how many step-fathers are perpetrators of sexual abuse, I don't know what it is exactly but someone linked it on here once.
Or do you find it hard to believe that you would struggle to instantly believe the man you have spent however many years in a happy marriage with, a man who has looked after your children as his own etc etc, has actually done something so abhorrent? Well actually that's pretty naive as well tbh, given the amount of people who've posted to say their own mothers didn't believe them when they 'disclosed' (i hate that word, but it's better than admitted I guess)
I for one haven't told my mother my step-father sexually abused me, cos I don't think she will believe me, despite his being a drug addict and all round shit human being. She loved him you see. Love is blind, they say, and sadly they're right a lot of the time. Besides which it's hard to admit that you yourself have been deceived for so long.
HAW, sorry to derail your thread but that comment irritated me. Once again, I wish you and your daughter all the very best in getting through this.