I don't think your update follows from the information you provided. I think someonewrongonthenet asks a legit question.
Ehm... ok! Nobody said s/he didn't...?
I think observing how fast the "signs of love" develop is a useful heuristic in determining how fast they could dump you
In my case the 'courtship' phase, let's call it this way, lasted about two months. In your experience this is too fast or the correct time for assessing correctly someone's interest?
Some people are just addicted to falling in love, and when it starts to fade, will look for their next rush.
That's a new perspective... In my case I liked everything about her (at least, about what she was displaying), and I still think we had compatible lifestyles. I don't know if this is a good heuristic for being together, but from my point of view it doesn't get better than this. For her I cannot say, of course, but I don't think it was the 'falling in love' addiction: I was her second partner at all, but mainly it's at least suspicious that her 'rush' for me ended just about when a competitor showed up...
I could have been less blunt. I know it sucks to be dumped. I don't know your situation better than you do, just trying to provide helpful perspective.
Some people change their genuine love interest quickly, especially if they fall in love easily. Some people take different kinds of emotions more seriously than others. Many of these people are not predatory at all. If she's young, and you're her second partner, maybe she's just emotionally immature.
Information that surprises you is interesting as it exposes where you have been miscalibrated, and allows you to correct for that.
I suspect the users of LessWrong have fairly similar beliefs, so it is probable that information that has surprised you would surprise others here, so it would be useful for them if you shared them.
Example: In a discussion with a friend recently I realised I had massively miscalibrated on the percentage of the UK population who shared my beliefs on certain subjects, in general the population was far more conservative than I had expected.
In retrospect I was assuming my own personal experience was more representative than it was, even when attempting to correct for that.