Why didn't you attend the visit with her? Since it affects you both equally, that is. Seems like you would have been there to speak your mind and explain how her birth control negatively affects you.

Since you didn't, this is how you file a complaint against a physician. See the medical ethics section here on the AMA website and file a formal complaint with the licensing board for your girlfriend's physician's state. Linky: http://www.ama-assn.org/ama/pub/physician-resources/medical-ethics.page? Bear in mind that she should be the one to file the grievance, although you can certainly walk her through the process and direct her to complete your complaint.

It's likely that her gyno is employed by a larger physician management group, so visit their website for instructions on how to file your complaint about how your girlfriend was treated during her visit. Have you considering filing a malpractice suit? Class action, even? Because the complaint that hormonal birth control can have an effect on libido is rather common, though the jury is out as to whether or not the convenience of oral contraceptives outweighs the inconvenience of entertaining 3rd party complaints about patient health. At any rate, you have many, many options as to how to properly address allegations of malpractice, hurt feelings, or recreational outrage.

Also, direct her to call her GP and ask for a referral to another gyno for a second opinion. Explore all of the different formulas available, and consider demanding that she cease oral contraceptives altogether and employ a different method of birth control that serves your best interests.

Or just accept the fact that your girlfriend has made a decision about her healthcare that protects her self-interests and explore your options re that decision.