The best way to approach this problem is to approach your own habitual sex fantasies with the intent of changing them so that you will be able to contain them within the sexual realtionship of your intended marriage. How old are you? Do you know how you came to develop these sexual appetites that you consider to be outside of what most women would accept?
Some of your sexual imagination could be carried out in your mind while you are having sex with your girlfriend. A great many people of both sexes, if not most, carry on sexual fantasies in their minds at some points in their lovemaking scenes, and many of these interior fantasies are never shared with their partner.
And here's another important point about very "abnormal" sexual enactments. I had a man in one of my men's groups decades ago who told me that one of his girlfriends was so devoted to him that she wanted to act out every one of his secret fantasies with him. So he took her up on her offer, and he loved it--at first. But after not too many months he realized that he didn't even LOVE HER anymore, because he LOVED HIS SEXUAL DRAMAS MORE. Sorrowfully, she had lost her individuality for him and had become nothing but a sex doll. He had actually HURT HIMSELF by demolishing his love for her, because LOVE and SEX are not identical.
I'm 28 and have had most of these fantasies for a good majority of my life. I attribute a lot of these fantasies to porn and more specifically the porn I was able to my hands on at a very young age. And see that is exactly what i'm trying to avoid I'm glad my girl friend does resist my sexual appetite. I have been trying to curb my porn intake not that it is very much these days to say the least but I still can't help but to have these lewd fantasies.
I have to run errands--Post office, but I'll write more later to explain how to proceed step by step with remodeling your sexual fantasies so that they are compatible with what your partner can handle. It's actually GOOD that she won't do some of the things you want--tho it might be more compromise than you can handle in the long run.
Alright we'll talk later when you have more time. thank you for your input