That is a really long period of time. Did you try vaping? You can regulate the amount of nicotine in it.
My cousin said vaping is more dangerous than smoking because you need to refill it with liquid, which we don't know if that is safe. Although the smells of vaping are quite different than smoking, I still don't recommend vaping.
Maybe if someone wants to quit smoking, he needs to have a strong will to stop, and he must have control over himself to say not to smoke.
I think vaping is much more dangerous, there are some news about accident related to vape such us exploding of the device and etc. And also it produce more smoke even if the smell is good because of the flavor it is still can affect the human health.
I suggest if every advice and replies in the topic didn't work for you then i suggest you should go for a rehabilitation it will be more effective.