Bismillahir Rahmaanir Raheem
Al Jawaab Billahit-Tawfeeq
May Allah guide you through this testing time and keep you firm on Taqwah and Eemaan. Ameen
In your situation, I feel that the dream is brought about by your actions of communication to a non-Mahram (someone who is legal for you to marry) and the fact that it's what you've been thinking about before sleeping or throughout the day. Contact without necessity is clearly Haraam and blessings are removed in any actions taken thereafter such as proposals or even marriage.
I feel that nothing is more simple or clearer than to send a formal proposal to the family of the girl. As she already knows you, I advise that you do not text her nor propose directly as it can scare a girl. Approaching the family is the best method as it gives the girl space to think, consider and also it's more real when family is involved rather than when it's discussed privately and pondering constantly how to put the word forward.
Do not complicate matters by lengthy communications and conversations as Shaytaan will play with the minds and hearts and nothing good has ever come from such actions.
When seeing the family of the girl, you must make it clear about your plans of leaving the country too. Not doing so could cause problems when you break the news to them.
As I advise in every matter of marriage, do not under estimate the power and virtue of Istikharah. Many have made up their minds happily after Istikharah and this should be the first step.
Please also see http://qa.muftisays.com?342
And Allah knows best