Keep trying! You know deep down inside it is the right thing to do, and some day when the "hangover guilt" wears off, you will look back on this moment as "just a blip". Years from now, you may not even remember it at all.
I agree with everyone else, don't beat yourself up over this. Turn it into an opportunity to learn what your triggers are, and then hash out a plan to overcome your triggers. It can be as simple as avoiding a certain place or certain people, or it can involve going to a meeting, or it can be something else that you know will work for you.
Sometimes a small step backwards can propel you even further head than you imagined. Stay positive, and best wishes to you!