Teach a Woman to Be Sexual
Your girlfriend's "use" of sex in a relationship is something I've seen from a lot of my girlfriends, friends and acquaintances. It seems that the mid-twenties are a real rite of passage for women from just using sex to *wanting* sex. Girls are taught to manipulate their sexuality so that they don't get f**ked over by horny guys, literally.
When they start to mature further they get the drive that you and I and every other guy had thrust upon him at puberty. Some girls realize all this right along with guys but I think more have an education period where it becomes clear to them in their mid-twenties or even later.
Your girlfriend has never really learned how to enjoy sex, to think of herself as a sexual person or to experience the need for satisfaction on a regular basis. The reason she doesn't see this as the case is because she is used to controlling her sexuality instead of having it the other way around. She's got a grip on it and she always has so her overconfidence is blinding her to her lack of experience.
What can you do to help the situation?
Easy: Treat her as a sex-object. Praise her sexuality. Compliment her mercilessly and don't let an instant pass when you find her sexy without telling her. If she's washing dishes and is silhouetted against the window say, "My god you look incredible. Tilt your head back a little there. You look like the silhouettes in the diamond commercials. You're so hot."
Laying it on thick? No. You're just communicating. Positive reinforcement is a *proven* psychological motivator. Don't hold anything back.
My last serious girlfriend hated going down on me but I love going down on women so she felt obligated to reciprocate. She wasn't very good at it and I'd usually lose interest pretty quickly. I never said anything and would rarely make any noise. We kept on this way for a long time until I realized that I wasn't helping her at all. I demand that women give me direction when I'm going down on them so that I can make it good and here I am keeping my mouth shut when she could use some feedback.
I started praising her skill. I started talking about how good it was the next day. After about two weeks of this it became one of her favorite things to do and she'd go down on me before heading out to work in the morning.
Running with this epiphany I started complimenting her on her body and making sure to mention whenever something she did made me horny. She turned into the best lover I've ever had and now enjoys herself so much during sex that if she goes a week without a lay she turns into a maniac.
Is this a sure-fire guaranteed thing with you and your girlfriend? Not a chance. She may have a chemical imbalance or psychological issues that require the aid of a professional. I really doubt it though. I just don't think your girl has come to terms with the fact that sex is *for* her, not something she gives *to* you.
Communicating that she is someone capable of arousing deep desire within you is something you should do regardless of whether there's a problem or not and it could wind up being the answer to your prayers.