Past Messing With The Present

I previously confessed something I found out but now it is causing a problem and I could use some advice.
I have been married a couple of years and this is the 2nd marriage for both of us. My wife didn't like to talk about her first marriage other than to say her ex husband was abusive and not a nice person. I kept asking questions, especially the question of "why did she stay married 12 years if he was so abusive". Finally she gave in. She walked me into the garage, went through some boxes until she found an envelope. She opened it and handed me a few photos. They were naked pictures of her ex husband. And his dick was huge, it looked like a circus elephant! She told me she simply stayed for his dick...
I am only 5 inches long, so immediately you understand what is going on in my mind. "why is she with me"???
I kept prying about the abuse and slowly she gave me some specifics. He was mostly verbally and emotionally abusive, especially jealous and controlling. Apparently he was into bondage, discipline and sadomasochistic sex. The problem was that he took it to far, leaving marks and really hurting her on purpose. When she protested or didn't want go along with it, he would punish her by fucking her in the ass and not in the gentle way. The image of his huge cock in her ass is now burned in my brain.
Since we started dating and two years of marriage she has never let me fuck her ass. And I have begged for it! If she took him, why not my 5 inch dick? It has caused several arguments recently. I want to so bad. What do i do?