I also would want to know if he's said this outright, because that might be a different problem than if you are picking up on signals. I only say this because I have some personal experience with a critical husband (he's now an ex) and he would say things about my weight to distance himself for reasons of his own. It's definitely something you need to talk about if he hasn't said anything, and if he has, it's still important to clear the air a bit about what he really means.
For what it's worth, a man having a problem with a woman's weight, sexually, doesn't necessarily mean he has a problem with you. My husband now has always been very supportive and loving, even when I was at my heaviest. Now that I've lost nearly 70 lbs, though, he's fessed up that sex is better now, for a few mechanical reasons. After all, that was 70 more pounds, almost a whole 'nother adult, on top of him sometimes, or getting between us.
Maybe your husband is just a communicative sort, and let it slip?