I agree with Mouradiff. Sexual attraction is a very strong emotion, and if its not fulfilled by a relationship to a certain degree (which varies for each person) then they are likely to get frustrated and break up. I've seen it happen, though this is usually more important for males (hormones, social-pressure or whatever you think, it's still important).
"Not surprisingly, early research on pornography and marital relationships has found that frequent pornography use tends to be associated with sexually aggressive behavior, sexual deviance, decreased intimacy,decreased sexual satisfaction, and increased marital dissatisfaction." divorce.usu.edu/files/uploads/lesson3.pdf
Of course in the above quote they blame the porn as the problem, but as I see it, it is a sign of sexual dissatisfaction with your partner.
A relationship is a lot like a recipe: You can add a little less or more egg, or flour to your bread and it'll still be bread. You can even spice it up with seasonings that you like, but if you completely forget a main ingredient, it's probably going to taste like garbage.
Oh, and you're also cooking for two, so if they hate pumpkin spice, you shouldn't add it to your bread or they're not going to keep eating it even if you like it.