It's hard to solve a problem if you won't admit that you actually have the problem in the first place.
That is why it's so heartening to see that you understand just how dirty the things you did to that girl are, and just how filthy all the thoughts you have about sex are, in the pure, untainted eyes of the Lord.
Have you given prayerful consideration to cutting off the parts of yourself that make you stumble?
ps... I have a crisis of faith too, and I'm not sure what to cut off. I can't seem to remember why we believe that book comes from God in the first place. I know it does of course, it just has to, everybody thinks so. I just can't figure out why, and the more I pray, the less I'm sure. Perhaps I should gouge out my brain thru my nasal passages.