You admitted this is stronger than you. It is! That is what addiction is. Just quit today, and repeat the plan tomorrow!
Don't be so defeated. We have your back if you are a man of your word. You can keep a promise for 24 hours...right?
If so, get reading and educate yourself on addiction and what to expect. If you have family, involve them and show them where you hide your cans. Get serious and tell the nic bitch to fuck off once and for all.
She doesn't do anything. You buy a can and in return you feel guilt, lose teeth, risk cancer and look like a chump to non-addicts. She is a great lie and you don't need her today.
If you wake tomorrow, post roll and fight another glorious battle!