Regardless of your s** its not cheating at all, sorry to hear that. As long as you dont fetishize the story and stuff, i DONT BELIEVE ITS COUNTED AS CHEATING, yes tho this has sm** in it but I believe its not cheating. You are just reading a fictional story about two lovers and etc, of course your ex gf have their own beliefs and thoughts but from what I know this is not cheating and if my partner read this, its fine.