One of the most loving things you can do is let her go so she can find someone who wants what she wants, and is willing to give it to her. Better that a relationship end on good terms than bad - which is likely how it would be if you marry and then feel trapped. As much as I hate hearing a guy tell me, "it's unfair for you if we continue," it really is a compassionate thing to do.
The world opens up... when you do.
Oh, oh, can't you see? Love is the drug for me. ~Bryan Ferry
"Love is that condition in which another person's happiness is essential to your own." ~Robert Heinlein