you might enjoy reading Dan Savage's column, savage love. In one piece he writes,
"my advice to women with low libidos: You can have strict monogamy or you can have a low libido, ladies, but you can't have both. If monogamy is a priority, you're gonna have to put out, i.e., regular vaginal intercourse and the occasional tide-him-over handjob and/or b******, cheerfully given. If all you wanna do is sit there and eat chocolate, you're gonna have to turn a blind eye to lap dances and mistresses and happy endings and the return of trade, i.e., gay guys giving NSA head to straight guys."
in another he is writing about a foot fetish, but the request for sex fits in perfectly:
you're going to have to play the breakup card. It's the only leverage you have. Tell her that if she can indulge your fetish—happily and regularly—and take some pleasure in giving you pleasure, she might be "the one." If she can't or won't, she obviously isn't. (Not that "the one" is anything other than a destructive myth, but for the sake of winning this argument, go ahead and use it.)
Finally, SFF, don't let the girlfriend—or anyone else—tell you that you're threatening to end this relationship over something trivial. Sexual fulfillment is important, particularly if your relationship is exclusive. And the "triviality" of your kink cuts both ways: If your kink is so trivial, why not just indulge you then? And in a long-term relationship—or a marriage—one partner's sexual selfishness and another's sexual frustration rarely prove trivial over the long haul. They're more often grounds for divorce.
But first, you should have a conversation with her. You might be really pleased at how it goes. It's possible that she's been waiting for you to ask.
Good luck.