Same shit happened to me few months ago.
I myself is a very careful person who will analyze thoroughly before proceeding.
There's this one girl that I really like, she likes me too, from all the signs I would assess her as a 99.9% success rate.
I sincerely thought she's the one and I plan to spend the rest of my life with her, I feel very comfortable and good being with her.
After like a month or two, she started to give all sorts of excuses to avoid seeing me, I felt something is definitely not right when I invited too many times and she's still saying not available.
One day I finally asked what happened, and I don't think the answer is really the answer. I still didn't give up, I continue to do what I can, without being aggressive.
At the end nothing has changed, we're now a stranger, the worst thing is that I don't even know what triggered this ending, I was still analyzing why for quite a long time, but well, nothing will change too even if I DID know the answer, I moved on, my heart still misses her from time to time because of the good times we shared, I never had those good times before in my life, but still, nothing I can do, just move on, lul.
EDIT: Nothing can be sure in this world, my confidence backfired me a few times in my life, like I mentioned above, 99.9% success rate still can hit the 0.1% failure rate too.
People can leave at any time, sometimes you don't even know the reason.
I remember I always advise people that "not every question has an answer", but when the situation happened to me I go against this and seek for answer / closure.
What an irony.
Most likely she found better one and wants nothing to do with you.