Don't feel too bad - call it a day off, and not the end of another attempt. Just remember that you don't feel great afterwards, and maybe it'll put you off next time you feel tempted
Like I've said to you before I'm the same, my weakness is chocolate - I'm not great at staying off it, but I just tell myself I have to burn off anything I eat. Generally I can't be bothered doing an extra 25 mins on the exercise bike just to burn a bar of chocolate off, so I don't bother

For once, my laziness comes in handy!