First of all, I hope you'll talk with your husband's doctors about this; they may have some helpful suggestions, and in any case they need to know about it. I'm not a physician, of course, but sometimes after surgery the shock to our system or the medicines we take can affect our emotional outlook.
It's important too for you to try to understand what your husband is going through. Once he was active and in control of his life, but now he's no longer able to do everything he once did. He's probably afraid those days will never return, and things he's always enjoyed doing now seem impossible. He may even feel washed-up and useless, but your support and encouragement can do much to help him overcome this. The Bible tells us to "encourage one another daily" (Hebrews 3:13).
Whatever the reasons for his attitude, one thing is certain: God has not abandoned him. Life isn't always the way we wish it were, but God is just as present in the dark times as He is in the bright ones. We can depend on God's promise to be with us, no matter what circumstances we face. The Bible says, "So do not fear, for I am with you; do not be dismayed, for I am your God" (Isaiah 41:10).
God loves your husband; may you both discover this truth in deeper ways during this time. Turn to Christ and open your heart and lives to His control, and then trust the future into His hands. With Christ, the future is always bright.