Know why you're making a decision to "never do X again". Know what you quit. Visualize many times the way the thing you want to leave behind is doing you harm. Otherwise, when you make a theoretical resolution, without the visceral realization of the problem, you're going to come under its sway.
Don't say you're never going to see that person again, only to realize how theoretical your vow to yourself was. Failing to keep vows to yourself brings you shame and, in the long run, self-loathing. Take a hard, good look back. Write a scientific study with lab experiments in your mind for why your decision is final. Why "never" will stay "never". Without waving, stare into the darkness from which you want to run. See it, feel it and only then take your vow. So that, when that can-do-January feeling starts to weaken you can consult all the excruciating detail of how bad that THING really is and know why you will never, ever submit yourself to IT again.