I've met many kinky individuals over the last decade who were in a relationship with someone who didn't share their interests. It can be very painful. As a kinky person you can feel unloved when your significant other shows little interest in your sexual desires. You can feel as though your life is lacking or empty. Despite everything you do, you feel it is hopeless and you'll never be happy.
Despite all these feelings, I urge you to never cheat. Even though you feel hurt, you do not have the right to hurt someone else. You will regret it; you will not find the happiness you seek when you go about it this way. This goes for all forms of deceit, be it in person, sharing pictures, or online role-playing. Do not engage in any of this without the express consent of your significant other...NO MATTER HOW MUCH YOU FEEL YOU NEED "THIS" (whatever your this is).
So what do you do? You have needs; they're not met and you feel a crushing sadness. Decide if it is worth leaving the relationship. If so, leave the relationship, then seek someone to indulge your fetishes.
...How do I know this? Because I was you once and I made the wrong choice. A decade later, I regret it every day. I never want to cause that kind of pain to someone I love again. You don't either.