My girlfriend doesn't want to have sex
I have been with my girl friend for nearly 3 and a half years and we have not had sex. We started dating when we were 17 so I didn't really feel that her lack of sex drive was a problem so I gave her time. Maybe a year into the relationship I finally asked her to have sex and she said no, saying that she wasn't ready for it. I have been a patient person, I have given two more years to this time, repeating my question every month or so. A while ago I asked her for a reason for not wanting to have sex but she couldn't give me an answer. Again I tried recently but this time all I got was that she didn't like it.
It now seems to me that it is hopeless, I have tried everything I can think of to try to persuade her but still nothing but I don't want to break up with her. Can someone shine some light on the matter?