During the relatively recent tobacco scandals, I was impressed with a comment made by a high-ranking tobacco executive and quoted in the Wall Street Journal.
He said, "Nicotine is an addictive substance, useful in the short-term alleviation of stress"
As am ex-smoker, I knew that was exactly right.
Your son smokes for the same reason you do. And faces the same difficulty in quitting. Stop picking on him and playing holier than thou.
It's not a 'character issue'. Cigarettes are harder to quit than almost any illegal drug.
The only ball in your court is that, strictly from the point of physical addiction, it might be easier now than it will be at any other time in his life (because he hasn't been at it very long.)
On the other hand, from the point of view of stressfulness, high school might be one of the very hardest times in his life he will ever face.
I suggest you stop adding to his stress by shaming him about smoking. Let him know he's okay with you. And tho I know it will be very, very hard for you to watch, let him smoke in his home.
Then see if there's anything else you can do to lessen the stress he faces every day. And to help him be more creative in coping with it. (I'm sure this won't be easy for you as you cope with stress the same way.)
Maybe seeing your son smoke will better impress on you the words he has been trying to get through to you about it.
Like I said, quitting smoking is one of the very hardest things in life that most of us will ever have to do.
Really, really, really, really tough. But it is possible.
(Incidentally, I've heard parenting teenagers can be pretty darn stressful, too.)
Good luck.
And good luck to you both..