Well, let's see . . .
When I first met my husband I did smoke. I quit a few years later due to the skyrocketing cost. I went probably ten years not smoking, then began smoking secretly during a very rough patch we were having. I eventually fessed up and he didn't make a big deal about the smoking, but he was bothered that I did it secretly. After a couple of years of smoking, I quit again.
Now, I see his point. As he say's, I'm a grown-up and can make decisions as to what I am going to do. So, why do something secretly?
Great point.
Now, maybe that's what you need to tell him. That he's a grown-up and shouldn't have to hide such things. Then, maybe you should accept his smoking needs? (that does not mean you approve though) I wouldn't allow him to do it in the house. It just plain stinks up the place. That could be your one restriction that can be agreed upon.
Some people are sometimes smoker's. They aren't really hooked on it, it is just something they've found that they feel helps them de-stress.
It's really up to you how big of a deal the actual smoking is. The deception, well . . . that's because he didn't "want to hear it", basically.
So, maybe just affirm that he's a grownup and let him be one? Well, that's what my hubby did and I haven't smoked for several years now. Can't stand the thought of it actually. But, that's the way it works. At least that's the way it has worked with me.