At your ages, she has the right to be sure before committing to marry you. Yeah, sucks for you, but it's better than having her curiosity get the best of her after your second child is born and you're in debt up to your eyeballs.
You're both young - you need to sow some oats; she needs to gather some roots. Life can be tough when you're young and in love. We've all gone through it. Just remember - You can't make someone love you. It's out of your hands. File it under "Things I have no control over right now."
Don't sit around moping and waiting for her, though - tell her that if she wants to date fine - but the wedding is off - period. Not postponed - cancelled. And tell her that you can't guarantee you'll still be waiting around if and when she makes up her mind, and for God's sake, don't wait around!!!
Get on with your life and forget about her. Maybe in a few years you'll run into each other and the feelings will resurface. Don't count on it, though.
Put her behind you and find someone else. Rebound relationships can be fun.
