It's important to quit for health reasons as well as social reasons. However, Smokers deserve good medical care; the same care non smokers receive. For years I would not go to the MD because I believed I didn't deserve good medical care since I was smoking. I know people who have been refused surgery because they smoke. Notice I didn't say because of severe lung disease but just as a whip to "encourage??" one to stop. Some people don't realize that providing artificial consequences or instilling fear will not promote a healthy lifestyle. You will heal. It may take some time. Nutrition, a positive mind set, following post operative MD instructions will all contribute to your healing. I'm sure you know that diabetes may slow or impair your healing process. All the above will contribute to your healing. Don't get upset that it's too late. It's not. Your fusion will not fail because you are still smoking. The fact that your MD felt you were a decent surgical canidate says a lot about your prospects of recovery.
Take care.