I'm sorry to have to say this too, but as a (ex)smoker, I made that same promise to my hubby. It was around our 25th wedding anniversary that I finally quit. In retrospect I know now that I really didn't want to stop otherwise I would have.
It is difficult to quit, the physical addiction isn't the hard part but the emotional addiction is. When smoking is something you have done for the majority of your life, it becomes part of your life and everything seems odd without it.
There is a great website, whyquit.com that may help him to understand his addiction and why he depends on cigarettes. It was very helpful to me and many others. You do not have to join to read the articles.
Good luck to you both!
He has to be the one to want to quit. Addictions are strong and this one is hard to break. When he sees it no longer as a pleasant experience, it will be easier, but it has to be his way and in his time. The more pressure you apply, the more he will smoke. That is just the way it is. lol