First you need to make him aware that he is sabotaging what you are working so hard to do. Tell him you appreciate that he is cooking, but you find his cooking irresistable.

If what he is cooking is healthy, then have a little of that food but turn down the food that is not within your diet. Explain that when he cooks or brings food home you feel obligated to eat it. Tell him you will no longer be eating certain things but it is not a reflection of him or his cooking. It just doesn't work for your diet right now.

It is up to you what you put in your mouth, but I know myself how hard it is when someone is eating something that you love and you have to tell yourself not to eat it. Sometimes it's just too hard to say no.

I've gone through this with my DH but he never got it until he went on a diet for himself. Now he sees where I am coming from when I say I cannot eat that. He knows if he offers me food that I cannot eat it has nothing to do with him. In fact, he will continue to eat it but he doesn't offer it if he knows I cannot eat it.