Been there, lived it for 5 years so I guess I'm kind of an expert in this area. Problems like this are usually symptoms of something deeper, like what's mentioned
here.
My relationship ended with me leaving her, towards the end we were having sex maybe once a month. She had self image problems that had developed into an eating disorder and pill addiction. It finally came to me that she didn't want to get better, so I left.
Now that may not be the problem here, but I'd be willing to bet that there's some kind of problem causing this and the intimacy is just a symptom of it.