Men like to think in specific words. I would sit him down and tell him, look, when i tell you A, i want you to say B. I my case it works like this:
A) I am never gonna lose all this weight.
B) Yes you can, you lost 12lb already, and you will lose more.
It has to be said in a natural and convincing voice, and you need to smile then and say, you are so nice and supportive to me, and hug/kiss him, and not like so many women start 'no i never will, i eat so much and hardly ever move' because if you start on this note he will slip into his usual harsh phrases. What you ask him for is support, not honesty, if you know what i mean. Honesty an wait for the time when you are slim.
Remind him also, that during the day he meets X people, and he is nice to them, sure he can't be rude to his boss. And it's only his boss. Why should be harsh to you, who are his love, his wife, the one who he shares home with. Home should be a place of tranquility and peace. Tell him that you want to lose weight so that you can look your best for him.