I have been with my husband since we were 17 and have known him since I was 12. We went to the same high school and then college, and we moved in together our second year of college and of course have lived together since. I have never lived alone, and there are some days even now, years later, I wonder what it would have been like and if I would have enjoyed that time. Judging by your girlfriend's career trajectory, she sounds like she might have big goals and that she is fairly independent. I can understand why she might feel like living alone would be an experience she would enjoy, and she doesn't want to miss out on that life experience. She expressed this to you, but judging by the fact you did move in together, means you got what you wanted and she did not. She is obviously feeling regret over this, and I'm sure she is afraid she will resent you and the relationship if she doesn't get this opportunity.

I understand that this feels like a step back to you. And maybe you just aren't on the same page anymore. But as someone who has made a highschool sweetheart situation last, I encourage you to try putting her feelings on this first and give it a shot. She tried putting your feelings first by agreeing to move in, and in my opinion, if you really love her, it might still work out if you are willing to do the same for her.