Do you irrationally change your goal weight often?

I wasn't sure how to properly convey my situation in the subject but I'll try here:

I've always been overweight. The most I've weighed is 202 pounds and the lowest, post-puberty is 160. I didn't stay at this weight for long as I got there through what was basically a two-month long starvation diet and after that I developed an over-eating disorder. It's the worst when I'm up against a deadline. I eat a lot of raw foods, at times 100% raw, but I'll get discouraged, thinking that I can't lose weight fast enough and binge on completely awful stuff. I'm now at about 180. And I'm up against a deadline. I've got 24 days until a trip that I'd really like to be a bit smaller for. Now, ignoring the the arguments about fasting and over-eating, I think I can get down to 160. The longest I've fasted was 17 days and I lost 18 pounds. That was a juice fast. I've also done two five-day Water Fasts where I lost around 10 pounds, so it is very possible that with 24 days of water/juice fasting (probably water only until before I go to bed - my biggest problem with fasting is not being able to sleep, but a bit of Sugar puts me out) I could get down to 160.

Here's where my problem is though: Sometimes, I think that 160 is a perfectly acceptable weight. I am 5'6" and very definitely big-boned. All of the charts I've seen that take frame size into account say I should be between 140 and 160. I would ultimately like to be on the lower end of that scale but weighing what is considered a healthy weight sounds really good, especially if I could achieve that in just under a month. I remember weighing 160. I felt good. I was a size 10/12 and for the first time in my life I could actually trade some clothes with my friends. I wasn't skinny but I was girl-shaped and I felt comfortable for the most part.

So that's how I feel when I'm being rational. 160 will be fine. A good starting place for changing my habits. Other times, however, I get really negative and just want to be skinny skinny skinny. I don't want to settle for 160. I want to be 140, maybe less. And there's a boy involved, which complicates things further. He knows what I look like but this will be the first time we've seen each other in a long time. I want to surprise him.

I don't know what I'm looking for from this post. Anyone relate?