I dont think you should feel guilty for having a little treat, I do every weekend lol I think you should praise yourself for how far you have already come and make your diet fun again, you may find thats all you need to do to get yourself back in the right frame of mind, good luck x
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2008 - 2011 Lost 87lbs
Maintain to 2012 - Then on to loose the rest!!
Week 1 (26/01) - -5.5lbs woop!!
Week 2 (02/02) - -2.5lbs
Goal 1 - Loose 7lbs - done! 02/02
Goal 2 - Get below 13st
Goal 3 - Loose 14lbs
Goal 4 - Get into size 14

Goal 5 - Get to target of 12st