I know someone who went through this. For 5 years her gf didnt have any desire. It seemed as though once they made a comittment and moved in together the gf just "lost" it.. Was severely depressed etc. My friend stuck by her through it all.. Frustrated, always true. But they worked through it and everything seems to be fine. They are back to having sex like they used too again. But it was just a matter of changing her depression meds...
I hear all the time of this. I havent been in a long term relationship where we were together for years on end . So I cant relate to what you are saying personally. But know all about and sympathize with you from hearing about it from my friends. I do wish you best of luck.