Mifatfait,
I think the answer lies in the difference between abandoning a chet in the normal sense, vs. recovering from an addiction. If you're "just" doing teshuva, it may be helpful to say "I'll never do it again. Not today, not tomorrow, not next month, never."
With addiction, this same thinking will backfire. It's just too unrealistic. Too intimidating. Too presumptuous. Because recovery isn't teshuva. It's a day-to-day, sometimes moment-to-moment gift from Hashem. Teshuva comes from me, from my willpower.
Recovery comes from Hashem. Your only hishtadlus is to turn the battle, turn your will, over to Him. When you detect the desire to act out, give up that will to Hashem. Tell him you don't want it. Not that you don't want to do the thing. You don't want to want it. Rather, you humbly pray that His will becomes yours, that you replace your diseased will with His. That happens one day at a time.
In reality, all of life happens one day at a time. This is one of the greatest lessons I learned in recovery. I am grateful to know it.
Have a wonderful journey,
Alex