Well, I was engaged, looking at apartments for after graduating so me and my fianceé would move in together after marrying (we even had the date set). We had been together for 5 years, from 18 to 23, I spent most of college with her (and thus, NOT partying like I should, yeah, I know). Then, out of the blue, she doesn't want to marry me anymore. She instead wants to leave the country, ditch her family (her father had just died, and she became the balancing center of the family, quite a burden) and never look back. Since I DIDN'T want to leave, we parted ways. You can imagine how I fully understande you. That was 3 years ago. 3 years from there, I'm ALREADY married (fell for an old friend, what can I say?), I graduated, we have our own place (although we still rent, no use in buying something when I'll be moving in 2-3 years to a WAAAAAAY smaller town - hopefully with internet access) and life couldn't be better, one professional opportunity after the other!
What I mean is: live your life. I commend you for wanting to stay close and be friends to her, but from personal experience, it hurts like #$&*@!. Take a step back for now, don't keep hanging out with her everyday, etc. Go live. Let time go by and see what happens. Perhaps she'll miss it like you do, perhaps she'll meet someone, perhaps you'll meet someone, perhaps she WILL miss it and YOU won't anymore. A lot can happen, just don't stop living your life.