Well...here's the hope for you in this situation..while smoking is wrong,and it can be frustrating that you have a hard time quitting,at the same time, let's take a look at this. The Bible says Jesus died as a substitute for sinners, that the punishment God put on Him was in our place, that we should escape.Practically all Christians "fall back" at times,, but if they lost their salvation every time they backslid, NOONE would be in Heaven!After the Rapture, we get our new perfect bodys,but now, we're still in the old ones we got from Adam and Eve,therfore imperfect. An addicting drug like nicotine can't influence us in the new body, but now, like any other sin...So I say, yes, you should try to quit, at the same time, as for losing your salvation over it,as long as you still in your heart put Him{which, based on the way you talk, you are a believer..this sin was put on Jesus at the cross,along with the others.If you came to God in the first place, and still a believer, I'd say you're still there with God. I think to lose salvation would be more like if a Christian walks out, like says,"I'm through with this, I'm following the devil now." A Christian who still has an ongoing sin in his life, I'd say God judges the heart,more than the action.The fact that you don't like it, and are frustrated and mention you're frustrated because you think you've failed God, to me shows you're disapointed over the right things.