Why doesn't he just admit it? ?

My bf says that he doesn't want me dressing "slutty". He says that I should not be wearing low-rider jeans/pants so that when I bend down, you can see skin from my lower back. He also says that it's slutty if I wear low-cut tops because of . He claims he is not insecure, he just doesn't want to be seen with a "tramp". I don't think that's true. I think he just doesn't want other guys looking at me because he's insecure. Why doesn't he just admit it? Why is it so hard for a guy to admit when he's jealous?