First off, there is no way to tell your husband you are not attracted to him anymore with out hurting his feelings. In this situation you have to put yourself in his shoes. What if the situation was reversed, you were the one whose weight was turing him off and he told you he wasn't attracted to you anymore. How would that make you feel?
Secondly, have you tried getting him to work out with you? You can always say something like, "Hon, it would really mean alot to me if we could start walking together in the evenings." It could be some other activity as well, swimming, going to the gym or something like that. If you work out with him and support him in losing weight he might be more proactive towards it.
I"m not sure who does the majority of the cooking in the house, you or him, but you can also start creating a more nutriential diet to help him lose weight as well and he might not even know your doing it.
I hope this helps!! Good Luck!!!