Ah Sweet Mousie...I know exactly what you're going thru, I have two brothers and a sister that are overweight (more so than your hubby) I, myself weighed 300 lbs last year. You've told him and his doctor told him. He's not going to do anything until he's ready to...and it will probably take being really scared for him to do it. Problem with that is, sometimes if they wait until they're scared, it's too late... :(
Sit down and have a chat...tell him that you're not going to tell him anymore....that you know he knows what's good for him and what's not, and that you're sorry he doesn't want to stay with you longer than what he's going to if he doesn't start to watch what he eats. Then sit back and watch, and don't offer any suggestions at all...not even if he asks. I'll bet that it doesn't take long for him to do it on his own and start asking you for healthier foods! :)