We've all been in your shoes, but you hopefully already know that. And hopefully you also know that THAT is the reason this site works....those of us that are here and giving you advice are passing on the same advice we recieved only its been tweaked here and there by individuals to make it work for them.
Here's a little piece of advice I'll pass on to you as I confirm my 1096th day of quit - that's three years.
Your title said, "The Road to 100." I'd ask that you drop that idea. Don't set your goal at that. Your goal, for now, should be, "The Road to Tomorrow." Commit yourself to the quit today. Just enough to get to tomorrow. Tomorrow, repeat your goal. Guess what? In the course of a week you will have 7 VICTORIES - you yourself said, " I think what has caused me to fail in the past is convincing myself that if I can quit for a month I can quit whenever..."
Prove to yourself that you can do this. A day at a time still adds up the same as if you were to have set your goal at 3 years off the bat. Except you build confidence and trust in your quit with each success. Quit each day for that day. Do that, and we're all quit with you.
You've got this. We've got your back.