Problems..

Clearly she doesn't place the same importance on your relationship that you do. She may consider you only a friend. There really is very little that we can do to make someone fall in love with us. It either happens or it doesn't. Of course there are many things we do that pretty much guarantee they will not fall in love with us so what we need to do is try our best not to do any of them. Any time you go into a relationship you need to first look at it as friendship only. If you can become best friends and everything else is there that will make love happen it will. The harder we try to force that they less likely it will. Consider what you feel like when you meet a girl and date, and you like her but right away know that she is not for you. No matter how much she may really like you that will not change. This is very important to understand because this may very well be where you are with this girl. The only thing to do is sit down with her and find out what is going on. You will never know unless you do that one very simple thing.

the only options you have are to either, tell her how you feel, or just walk away and let it be. i wouldn't do anything to purposely try and break them up, because i think that's wrong, and the guy she is currently with deserves just as much of a chance as the next guy. if you tell her how you feel and she decides she feels the same way about you, then she can make a decision and take action about it. there is nothing else you can really do. i'm sorry things haven't worked out for you the way you wanted them to.