I am probably the last person to give you relationship advice here given my ego and pain body but, let me try.
First, read some ecky bro. Preferably, Stillness speak. I feel like that read is just something I can read one small piece and take so much away sort of like Psalms.
With respect to this girl, attachment is natural part of human nature. It is through suffering; desire, materialism, wanting that leads to suffering and or pain. We associate self with whatever we attach to and to detach from what we cling to leads pain.
I never understood why people got all sad on reality tv shows, movies or documentaries when leaving somewhere at the end of a trip. It wasn't until I began to explore and travel the world that I really got it. It pained me to leave knowing my home was somewhere else but, I got attached to a beautiful girl, to living like a rockstar, all inclusive vacation, no work, no bills, no problems but its pretend.
I had three days with this girl on one vacation. She was very special to me because she was the first girl I really hit it off with after my ex gf. I still am close to her today. Another girl I met when I traveled across the country. To this day, if I ever met anything close to a soul mate, it would be this person. Like you, I cannot leave behind my family and life obligations at the time being. She would have to come here for now anyway. She has her life. I have mine. We keep in touch (social media, snapchat, fb etc). You never know what the future holds.
You are twenty-one. I met her when I was younger then you are now. You both will grow older. I know I have. Who knows. Maybe she will come visit. Witht he net, the world is not the small a place anymore. I am sure you have more to experience.
Enjoy the time you have. Read Way of The Superior Man By David Deida (Download PDF online). What you feel she feels. If you are confident, she feels it through your action, your leadership, and call to action. If you are weak or mediocre, she feels this too. What is love? The most precious thing you can share with her is time. Share that with her and make the most of what time you have left.