When I quit smoking 15 or so years ago, I found that the hardest part of it wasn't so much the addiction to nicotine but the habit of the cigarette. The first few days were excruciating -- going through withdrawal while still going through my days as I had before, with all the triggers tormenting me -- drinking coffee, dinner out with friends who smoked, talking on the phone in my office, reading, watching tv... I then decided to turn my world upside down for a bit. Obviously, there were some triggers that I couldn't not do, but there were several that I could eliminate for awhile and replace with non-smoking activities and/or places. It really did help -- 2 or 3 weeks and I found that I could read the newspaper at the kitchen table without really thinking much about having a cigarette. I certainly didn't automatically reach for one. And gradually I brought my normal life back, though it was a very long time before I could even drink coffee again, let alone drink it without thinking about cigarettes.
When you're ready, would it be possible to get away for a week or 2? Not far, necessarily, just away from the things and activities that trigger your desire for a smoke. Ideally someplace where you can be active.
The other thing I did was, I think, peculiar to me and the way I think. I find that if I try to deny myself something, I want it even more, so I carried an unopened pack of cigarettes around with me. Having them there in case I ever wanted one brought my area of control down to one small impulse, and that I could do. Having to control the whole going to the store, buying the cigarettes, opening the pack and having a smoke was too large for me, I think. Anyway, whatever the reason, it worked for me.
Another thing you could do, as I think about that sense of overwhelm, is to chunk it down: first day, you commit to yourself that you're not going to have a cigarette until 8pm. Do that each day until the daytime habit is completely broken, which may take weeks or even months. Then you commit to not smoking during the week at all (though you can view Friday after 8pm as the weekend :)). Or whatever chunks work for you. Some people prefer to just whip the BandAid off in one pull, other people prefer to ease it off gently -- they all get the same result in the end.
Don't beat yourself up for giving in to the urge -- it may take a few attempts, but you'll get there. :)
