While I wouldn't say you're a prude, but you definitely have a problem with porn and perhaps even have self esteem issues. As a guy who watched porn for years and had a fairly strong addiction I can say that I wasn't playing scenes in my mind during sex. Everyone is different and watches porn for different reasons. I did because sex is/was very sporadic. My best friend watches porn because he likes the idea of being able to "have" any woman he is watching without any emotional attachment. I can't say whether he plays back scenes while having sex with his wife, but he has never said anything close to that.
He has some issues too, probably self esteem also from the sounds of it (along with the porn addiction, if indeed he watches as much as you lead on). Bottom line: either learn to live with the porn, tell him to really limit the porn watching because of how it makes you feel, and definitely DEFINITELY get out of there if he even gets close to cheating again.
...one can be sure of nothing until it has already happened...