I can relate to your post! Whenever I'm in a new enviornment, I seem to not know what to do! I want to eat and eat because I feel out of control. I don't have all my usual foods, equipment, gum!!! or whatever it is that I typically rely on to stay on track. The worst is when I go to my parent's house because there's something about my childhood that takes over. I guess I used to eat a lot as a way to rebel...do what I want when nobody was looking. I guess some kids did drugs, and I did food!
Anyway, now that you know that stress and being away from your usual environment messes w/ your efforts...now you can do something about it. First, forget about messing up. It's in the past. YOu're doing amazing on your diet so you obviously can do this! Second, next time...be prepared. Bring a workout dvd or do resistence exercises. Or, crank up some music and dance like a crazy chick!
Bring gum w/ you, bring premade snacks and meals. Take a good book...maybe one on weight loss?
If you're having a fight w/ your mom or anything is bothering you, maybe write in a journal? Punch some pillows...do anything but eat too much!
Anyway, this is all advice I have to listen to myself, but I hope it helps you a little.