If you have once been a smoker you will never be a non-smoker, only an ex-smoker. My husband, quite a heavy smoker from a young age, gave up smoking following a stroke about six years ago. I, a very heavy smoker from a young age, gave up smoking two years ago because I wanted to. Both of us get the occasional desire for a cigarette, Mr absent more than me, but don't have real cravings. However, we are both aware that if we hit a real crisis, we might be tempted turn to cigarettes for comfort. I have a friend whose mother hadn't smoked for nearly ten years and following a a ghastly even was offered a cigarette, took it and went straight back to a 60-a-day habit.
Nagging and being threatening – if you don' stop smoking I'll leave you – won't work and will merely cause resentment. Besides, do you really mean that? Horror stories about the results of smoking won't work either even though there has already been smoke-related illness. Quite a lot of the time people don't believe in their own mortality. Calm and loving discussion might work. An E-cigarette, which is tar-free, could help.