Please tell me how you stay motivated!

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All of January, I was super motivated and doing great. I wasn't incredibly active, although I did increase my activity. I ate really healthy things, and at the time, I was enjoying those things. I had an amazing amount of will power. When I ate out with friends, I was highly calorie conscience about what I was consuming. If someone brought junk food into my house.. Nope, it wasn't even an option for me to have any. After a month, it became a little more difficult and I gave myself a cheat meal once a week, which turned into a cheat day once a week. And that leads us up to now. This past weekend, I went on a family vacation. I received tons of compliments, which made me feel very bashful. However, I was proud of myself. So I said "What the heck, I'm on vacation." Turned into a greasy fried chicken cheat weekend. We came back home Sunday... I've been doing horrible diet wise ever since! BTW- I went from 166 to 151, and for some reason, I can never stay motivated long enough to get into the 140's. So please tell me, has anyone else gone through these same things and still succeeded/is still succeeding?? Why does it become so difficult once I start feeling better about myself to maintain my loss and continue on?

Before pic- <a href="http://imgur.com/UeWdg"><img src="http://i.imgur.com/UeWdg.jpg&quot; alt="" title="Hosted by imgur.com" /></a>