I'm not sure what kind of comraderie you were looking for, but here's a suggestion. Maybe if you changed your diet, shopped for healthier items, and cooked smaller portions, he would reap the benefits of your committment to changing your lifestyle. Sure, I'd love a second plate of spaghetti, but if I already had a serving size, then I'll just have to fill up on salad and vegetables or some lowfat popcorn later.
Sorry, I'm out of bacon and eggs, but here's a bowl of Total. If he has an extra value meal for lunch every day, overlook that in the beginning. Forget the Oreo's and have fresh, washed fruit in a bowl on the counter, ready to go. No chips or Dorito's, but have microwave popcorn in that spot. (Read the label on the popcorn before you buy it - some of that can be wicked too!)
Portion control (just don't cook as much) can have an impact on his weight. Maybe, if he sees a slight reduction without realizing the changes you have made, he'll be motivated to try harder. Point out the reduction in your own weight that these subtle changes have made, as motivation to him.
Forget the soda's and buy water. Get a Brita pitcher for the fridge. That way, chilled water is always ready to go. Drink water instead of something with sugar in it. If he drinks alcohol, it might be tougher to find a way to scale back on that without him being committed to losing weight. (Alcohol=sugar!) Water will also curb your appetite.
Being a disciplined person is very difficult. Most people are not willing to do that until they have a major event to wake them up.
You don't want to turn into his mommy, because that will backfire on you. Just make some more transparent changes and maybe the results will bring about more change and improvement, and become motivation for bigger changes in the future.
He didn't gain 150 pounds in a year or two, so losing it should be a long-term project and not a crash diet. If he needs to lose 100 pounds a year from now, and 2 years from now he's trying to get that last 50 off, then you will have succeeded, he won't be as tired, and the likelyhood of being a younger widow will be greatly reduced!