NTA

But the fact is that weight and obesity have a direct correlation with morbidity and quality of life. If he's gained a lot of weight, maybe he does need some help going in the right direction.

I really do like that your MIL brought up her concern that he'll die early, because it is a reality. Go get a physical checkup from your family physician with your husband. If he mentions your husbands weight or cholesterol, use that as an excuse to eat healthier and all that.

Once the weight starts to go, he'll feel much better and will be happier he has some of his agility back. Trust me!

Also, as someone who has gained and lost weight in his relationship, having a partner like you who will always say I look great was so crucial. Your husband is a lucky guy!