Here's the background. I am 5'3 and used to be a size 10 pants and 150 lbs. I changed my diet and lifestyle and I'm now a size 2 and 120 lbs and my boobs are still a 32DD, although my booty shrank which I am self conscious about. Anyway he makes jokes calling me "fatty" and he questions my eating even though I eat healthy and monitor my calories. Why does he do this? He should be proud of me and make me feel beautiful.
5'3, 120 lbs, 32DD. Good. FREAKING. God! You are absolutely perfect. AND you have a high sex drive?!
You should sit him down and tell him that what he is saying bothers you and makes you feel badly about yourself. If he cares about you (and plans to spend a lifetime with you) he should knock it the hell off. If he doesn't. . . I refer you to the top of my post. You will have NO problems replacing him with someone who will treat you better and be MORE than happy with your body!
Maybe he's just being sarcastic? As in, teasing you playfully? It all depends on the tone of voice he used :)
But to me it sounds like he's being sarcastic because you're so much thinner, so he calls you fat to be ironic, which is actually an indirect way of complimenting you. Once again, it all depends on his tone and the context.