He's a guy, he sees clothes, he thinks you have clothes. Get rid of them! That way you can't go back.
JulieL has a great idea with the cookbook. There are some excellent suggestions here on the forum, too, print out something you think you'd both like and leave it on the counter or give it to him with a little hug. If he's insecure because you are looking better, maybe he needs to know you aren't dumping the weight preparatory to dumping him.