You can have all the insight in the world as to WHY you do something but to actually change behavior is another matter.
Cemar - you stated that your W "hurts" you when she says no. I'm sure she is aware of this fact. Why does she do it?
Maybe she is passive-aggressive. She can control you in a sense by rejecting your sexual advances, without having to deal with underlying issues, resentments, etc.
It is simply easier to follow the same "habit" of saying no than changing long ingrained behaviors.