Some of us eventuality find ourselves with a significant other that is on a completely different wave length in kink or sexually in general. This kind of situation leaves a bit of a vacuum for desires and kinks that our SOs don't share.
For some of us our SOs are open and understanding enough to agree and support us in finding other play partners that share similar interests. Unfortunately the success rates of finding play partners with like interests, at least in my experience, is quite low. You can probably find a one off kind of situation, but unlikely to find anything regular or consistent. On top of that, at the end of the day, they aren't your SO and your primary person.
The other option is to live without or watch copious amounts of porn. Porn is never really satisfying more than temporarily, and well living without really isn't fun for anyone. For many though, these are the only real options available to them. Most people aren't open to having open relationships or outside play partners in any capacity.
The rare third scenario is when your partner isn't into it, but is willing to give it a go anyways because they know that it will make you happy. This scenario starts out great and hopeful and maybe you can introduce them to this kink that you're really into in a way that they enjoy it too and then everything would be perfect. Again it doesn't take long to realize that is not the typical result for these kinds of things.
Sure there are people out there that really don't care if their partner is having fun and that might be part of the fun for them. But for those of us that want our partner to buy into and enjoy what we are doing, and be an active participant because they want to be, the first uncontrolled facial expression or adverse body language that you see typically puts a huge damper on things and changes the entire mood.
In all likelihood these are just things that some of us will have to figure out over time how to deal with on our own. There is a reason why these thoughts and fantasies are referred to as our darkest. They are probably meant to be kept to ourselves.
Even if we are comfortable with being completely open with our partner about these things, if we were to write the a note or a letter explaining all of the fantasies we have floating around in our head. If we wrote down all of these dark twisted screwed up things that we wanted to do with or to them, not just the things that we have touched on before, but the deep down dark things that you don't openly admit. What if they reject us? What if they read it and you see fear and disgust and disappointment on their face? There is nothing worse in the world than experiencing that.
So we continue on moving forward thinking often about the fantasies that will likely never happen, at least not with your person. Because at the end of the day, what else is there to do?