I think I know the feeling. I felt that 'its done for good' moment when I quit three different drugs in the past (crack, hallucinogens, opiates). They happened at different times but in each case I just said I was done and that was it. Havent touched any of em for 5 plus years and never will.
For me alcohol proved different. I have spent much time trying to force that feeling but it hasnt happened. I finally came to the conclusion that legality may be the difference in my mind. Alcohol is so socially acceptable its hard for me to kill any 'lurking notions' of drinking in the future.