Taking care of yourself, trying your best to stay healthy, trying to make your body “a temple of the Holy Spirit,” is what we all should be doing. But addictions are hard to break and most of struggle against one or another at least part of our lives.
There is a great book called Addiction and Grace. (Don’t remember the author–it’s from the 90’s or so, I believe.) His bottom line, and what I’ve discovered to be mine, in my own battles against addictive behaviors, is that you must pray like crazy for God’s Grace to pull you out.
Naturally, you have to do the footwork. Throw away those cancer sticks, no matter how much you paid for them. If you end up buying more and smoking one or two, then throw the rest of them away too. (I remember drowning what was left of a whole carton in the dishwater once!) Get some help, some support. Call the Cancer Society and start there to hunt for free resources to help you. Buy some nicorette if it helps. Anything. But just keep at it. I quit smoking a million times. But then one day, I actually did.
And calm your troubled soul. Worry less about whether or not it’s a sin, and more about praying for God to help you. Jesus Christ has already relieved you of the burden of your addiction, you just have to get around to believing that. Talk to a priest if you can, he might be able to comfort you and guide you.
Good luck, and God Bless…