After 7+ years going on and off the gym I can tell you one thing- if the motivation isn't coming from within, you won't do sh*t.
Oh yeah this is true, so much of my friends dropped the ball on getting healthy just because their friends who pushed them to workout, stopped. Then they suddenly had no reason to get fit. Since you know your husband the best, try to motivate him to get healthy for both of your sakes especially for himself. I myself took a good hard look in the mirror and I didn't like what I see. I had a BMI of BIG FAT YELLOW RICE BALL (please laugh, I've actually been called that ).
From experience, I would like to point out dieting is not what it seems based on general consensus. It's not about eating less or starving yourself to lose weight. It's more about eating healthy as well as eating stuff in moderation. Except for fruits and veggies, you can go all out in that. Giving up or changing your eating habits is very tough if you have random cravings like me. It's better to ease it in.
But with all the great advices from this thread, the only way we can help him is just showing him the way. Remember, he must take the first step by himself!