You bring up a good point, in that sometimes, even right from the beginning there is dysfunction in the sexual relations. This can be for many reasons.

I've personally known many women brought up religious who are told "sex is bad" for so long that when they get married, they aren't able to turn that voice off. They have internalized that sex is bad.

There are also many people - women too - who are asexual and simply have no desire.

In your case, your relationship sounds very one-sided. There are indeed women who are willing to take, take, take and never give anything in return. This is not healthy and I would not recommend staying in the relationship, especially since there are no children to consider.