You have three very good reasons to give up smoking. The negative impression on your SS, relations with his DM, and for the sake of your own health.
Frankly if you are really smoking just 5 a day it shouldn't be that hard. If you really aren't prepared to contemplate giving up for the above very good reasons, wearing a nicotine patch for two days a week is not a lot to ask.
I smoked for 3 decades, gave up two years ago. Believe me, it doesn't get easier to give up, it just gets harder and harder. So do it now.
Whether or not your SS sees you smoking at home, he'll smell it when you walk back in the house, on your clothes, your breath, hands and hair. And boy does it stink. As an ex-smoker I'm amazed how strong and acrid the smell is, even if you just walk past a smoker, or one walks in the room.
If you're smoking in front of him on days out, whether in the open air or not, I would be very unhappy about it if I was his mum.
So what if she hasn't complained about it until now? Maybe your SS has begun to notice it, and told her he doesn't like the way you smell. It was around that age that my DD started to fuss about the smell and get irritated about me disappearing!
You also need to bear in mind that he is at an age where they will be discussing smoking at school, in an extremely negative way.