I can tell you my own experience, I had Long d with my gf for 4 years, we said we would wait each other, we did. But at last i decide to stay here in the US for further study, we broke up. Not that i am not love her or wht, i still love her very much. We break up because she doesnt want always eagering a bf beside her but I cant give her any. She decided to keep our relationship as friends. We passed through a lot during these 4 years, we know we both love each other a lot, but then, it's really hard for my gf to wait another few years again.
so we break up after all these challenges. All of my friends no matter in HK or US felt shock to our seperation because we were really a pair of very sweet couple. No one can believe it.
What i want to say is that.
If you really want to keep this relationship successfully. It's really tough. At last you may end up with the result you didnt want. As no one knows the future. Maybe she will be like me, after 5 years, she want to stay there for further study or work. It's too far away from now to say you MUST wait for her i think.
I suggest that you keep her as a very close good friend in all these years, sharing each other stuff. If she really comes back then you two get back together. THis is because i think that in all of my 4 years with my gf, our lives are very restricted, as you are in a relationship of a pair of couple. After all these years, I really notice that having our own lives is really important for a developing relationship. Many things needed to pay a lot of attention, need to get a balance in your care to her and her own development of life. Trust and honesty is really important.
I did knew few people did pass through all these Long distant challenges and get marry at last. but most of them cant last long. Start this kind of relationship need enormous tolerance, communication and understanding. For both of you it's really a tough challenge. Dont start this unless you two have the same goal and enough faith.
Good Luck, you may ask me if you have other questions, I am willing to share.