Not trying to be a dick, and I haven't dealt with any addictions myself, but man up, don't make excuses for yourself, and make that tin you just finished your last. Deal with the withdrawls for a couple weeks and be done with it. It's mind over matter here and nothing more.
That said, I'm glad to hear you want to quit, and I truly wish you the best of luck!!!
I have only dipped a couple of times, but smoked for 9 years before I quit 5 years ago. so I definitely understand addictions and the quitting process.
I tried several times to quit and was unsuccessful until 5 years ago.... The difference was that I quit when my wife and I decided to have kids. At that point I wanted to make a change in my life to make life better for my kids (big motivation). until then I kept making excuses as to why I could not quit.
when I did quit 5 years ago I simply stopped buying them. I smoked the last of my smokes and when they were gone, they were gone. Life sucked for about 3 weeks, I was grumpy, easily irritated, felt like I had no energy and I was coughing worse than I ever did when I was smoking. I had a constant craving for a cigarette, but just kept fighting it off... after the 3 week mark, I started to feel the extra energy and the grumpiness started going away and life started to get better... now I almost never get cravings, although, once in a while (every 2 months or so) I get a VERY easy to fight away craving.
I guess my point is, find a GENUINE big motivator and REALLY WANT TO QUIT. Make a decision to quit and stick to it.
I have been smoke free for 5 years and looking back, it was the best decision I ever made and I was STUPID for starting to begin with.