What is the ruling on imagining sexual stories during marital intimacy, and is it permissible or forbidden to view images included in these stories?

Your feeling of distress about your condition is the beginning of correction. The first thing we advise you to do is to supplicate and ask Allah for well-being. You must be sincere with Allah and have a desire to rid yourself of this habit. Strive to stop recalling sexual fantasies, and instead, appreciate Allah's blessing upon you in your husband. Remember that "Knowledge is gained through learning, and forbearance through striving to be forbearing."