People often dispense the advice "follow your heart" to folks who are in situations like yours. On the surface, it seems plausible. You say you are in love with this girl and it is only natural that you want to be with her. It is also only natural that you want her to reciprocate your feelings.
You're In Different Places
However, I will say to you that you need to evaluate your relationship much more closely. From reading your letter it is obvious that both your hearts are in two different places. For a relationship to be successful, there has to be a degree of commonality. At the very least, both people need to be ready to take the next step together.
The simple thing to do would be to stay where you are and hope that one day she will be ready to commit to a more serious relationship with you. What you need to ask yourself is, "how long am I willing to wait"?
We could be talking about a serious amount of time here. Do you think it will be worth it in the long run? Only you are sufficiently able to answer these questions.
It May Take Her A Long Time To Figure It Out
I don't want to take the cynic's role in your issue, but from my own experiences it usually takes career focused people many years to realize that they've fumbled the ball in other aspects of their lives.
You must prepare yourself for the possibility that she might never be ready to love you, or anyone else for that matter. It is a sobering thought I believe you need to deal with.
Generally, society is hung up on the ideal of their being one person out there for everyone. We are so obsessed with it we blind ourselves off to the fact that there are actually many people who can be right for us.
Given how your situation is standing right now, you need to leave yourself open to other experiences. Who is to say that in time you will not meet someone who makes you feel the same way she makes you feel? Do not place yourself in the position where you limit your own potential.
There is nothing wrong with wanting to be true to your feelings. There is nothing wrong with just wanting to be with one person. Devotion and fidelity are not profane words. Monogamy takes a strength of character that many just do not have. It is very difficult to be fulfilled by these things when your partner's head is in a different place, though.
Date Other People
If you want to continue your relationship with this woman, do so. Maybe one day she will decide that she wants you just as much. In the interim, continue dating other people and do not close yourself off to the ideal of being with someone else. Do not allow yourself to miss another boat just because your current ship is stalled out in the water.
Be honest with yourself, learn your own needs, and be good to yourself.