Sounds like it's serious conversation time with him.
I would remind him of the support he offered pre-op. And I'd attempt to cover what his insecurities are about your weight loss. It's not at all uncommon for our partners to feel as though we're going to "get hot and leave them." So remind him of all the reasons that you love him. Tell him why you want to do this for YOU, your health, and how that will make you a better person for him.
And if you can find a common ground with all of that, ask for his support again. Tell him specifically what is a problem for you and see if he can go back to the support that he gave pre-op. Also, try to make him an accountability partner. Make sure he knows what the rules are from your surgeon like how much you should be eating, what your Protein requirements are, and what your calorie range is. And then tell him what you've done for the day including your workout routine. Sharing MORE of this journey with him may help to include him in the changes rather than leaving him feeling like he's not part of the loop, not important in your new lifestyle changes, and while you're doing this for you, helps him as well.
I wish you all the luck in the world!