I'm not a physician, of course -- but the first thing I urge you to do is to talk frankly with your husband's doctor about your worries. You are wise to be concerned, and his doctor needs to answer your questions.
After all, he knows your husband's situation, and he can help you understand what to expect as your husband recovers. It takes time to get over major surgery, and his doctor can help you be realistic about it. You also may discover that the doctor is already planning to change your husband's pain medication from time to time, which should reassure you. If you don't think the doctor is taking your concerns seriously, however, seek a second opinion. People sometimes do become addicted to painkillers after surgery, and you should do everything you can to help your husband avoid this.
At the same time, be an encourager to your husband. The Bible says, "Therefore encourage one another and build each other up, just as in fact you are doing" (1 Thessalonians 5:11). At times he may feel like he never is going to get better -- but he can, and you need to encourage him to do whatever he needs to do to gain strength.
Most of all, let this be a time when you both find new strength from God. He loves you and wants to encourage and help you -- and He will, as you open your hearts to Christ.