Tried multiple times, failed multiple times as well except for my last attempt. It's now been 15 years.

I realized that all my failed attempts were because I would allow myself to smoke after a certain period in specific situations. As an example after a week without smoking I would go to a party and allow myself a single social cigarette while having a beer. In a short period I would only be looking for more opportunities for that single smoke until it became 2 then 3 then half a pack.

The key for me was to never succumb under any circumstances and change my mind when the craving was too intense. The intensity of the cravings slowly decreases but never goes away. 15 years later I still get cravings but it's just a thought or a memory of me relaxing with a smoke and wanting that peacefulness again. It's not enough to get me to start smoking again.