Thank you so much for your kind and thoughtful replies.
What makes it most difficult for me is that he doesn't feel he did anything wrong and thinks I'm overreacting.
This is such a private and intimate ordeal for me (my weight) and something I can only talk to him about. How on earth he could tell this to people when I have asked him not to is beyond me.
It's not like he said that it has been difficult for him and he needed to confide in someone. That I could understand. It's that he just matter of fact told it to someone without giving any thought to how I would feel about that person knowing something so personal about me. He must have known that I didn't want him to because at first he only said that he told him I was having surgery and not what kind.
I am sad and angry and after some yelling from both of us we are now not talking.