Living together and no sex

My BF and I have been living together for about 2 years and some months. We have a good relationship, at least I think so. I have a high libido but I just don't understand why we don't have sex. I know he masturbates everyday sometimes twice a day, but why he won't just have sex with ME? We have sex rarely, once a week and right now we're going on two weeks. Could he be losing interest? Should I just leave it alone? We've had fights over this and honestly I don't even want to bring it up anymore. Help.