I'm an ex smoker. I gave up about 11 years ago, just before I met DP, now DH :)
DH hates smoking and would never have dated me if he'd known me as a smoker!
I hate smoking too. I have two DC now and care about the effects of second hand smoke and the effects on my own body etc...
However, in the last 10 years I have had about 2 cigarettes a year (maybe 6 last year as it was a stressful year).
All of these I've had in secret because I wouldn't want either DC or DH to feel I had gone back to smoking, or to be ashamed of me. I don't want to the DC to see ever.
I have told DH about a few of my secret smokes and he said it's fine, it's my body etc... but I feel disappointed in myself afterwards.
I think the problem is that smoking is addictive. I started smoking as a child. I liked it. I smoked when things were bad and I felt better. Every now and again I go back to that cruch.
I'm lucky my husband understands and when I do tell him about the odd one I've hidden from him, he responds kindly and supportively.