You've taken the right decision by the sound of it. If she u-turned like that something clearly isn't right which is not the basis for a successful relationship going forward. I suppose there's always the possibility that there's something else going on in her life that has unsettled her, but then her explanation doesn't seem to suggest that.
Unfortunately the advice here seems right, time to end it and move on unless you have time to spare on a relationship that doesn't sound like it has a long term future (which as long as you know in theory it's not going anywhere is no problem either).
I'd be very surprised if within a day of ending it shes not back in touch with you saying it's cleared her mind, she didn't realise what she had til she lost it etc., for some reason people want what they can't have.
In any case, if you've got yourself into a good financial position, look to get yourself a good bachelor pad, focus on the future and a great start to the next chapter of your life. FWIW I concur with others here, when my now wife and I moved in together there was no hesitation or thinking about it, it felt right from the get go and was just a natural next step. If it's a tough thing for her to do now when it's supposed to be the most exciting thing and something you're both looking forward to, can you imagine what things will be like when times are tougher?!?
Good luck OP, hope it all works out well for you, you seem very mature in your attitude so I'm sure it will.