Am I wrong for not being attracted to my boyfriend?

My boyfriend and I are long distance for college and he joined a frat. Of course, the frat comes with a lot of drinking and he has since earned himself a nice beer belly. Along with that he never exercises and I know he'll just keep doing the same thing when he goes back in the Fall. I feel bad because I'm not attracted to him anymore and I hate having sex. He continues to not take care of himself and it doesn't look good. I feel like I'm being selfish but I don't know what to do. I've told him before and he says he'll change but he keeps drinking and eating unhealthy. I offer to exercise with him and make him healthy meals but he refuses.