Okay, please don't pick on me too much for this...

I'm a girl, and my boyfriend wants to have sex with me all the time. But, I don't really get any pleasure out of it and I don't know why, and it really upsets him because he isn't "pleasing" me. I find it to be just a bit painful, probably in part because he's kinda large.

The thing is, I actually enjoy masturbation a little. So if I ever mention masturbation ever, he always wants to know if I've been doing it recently, and I feel I have to avoid his next question, which is "Why don't you have sex with me then?" I've tried to explain that I just don't enjoy it, and he always acts all depressed and tells me that I would enjoy it if I was with someone else more attractive, and thinks I could just pick up the most attractive straight males on the planet just because I'm somewhat attractive.

I dunno what to do about this, and it causes so many problems. I'm wondering if something is wrong with me - I've never heard anyone else say they have this problem. And what should I do about it? I already pretty much accept the fact that I'm not going to like have sex more than once every week, but that won't fly with most men it seems. What should I do?