Sometimes when you're with someone for a very long time you become attached to that person above and beyond a romantic bond. The attachment is an everyday thing...a "this is the person I see movies with" or "this is the person who loves my barbeque chicken" type bond. Those are the hardest to get over.
There's really nothing that anyone can say to make you feel better. The only thing that can heal something like this is time. I personally am a bit confused when you say she "likes someone" and "is excited about getting married" does that mean that she is already engaged to someone else? No amount of "forget that bitch" is going to help. All you can really do is take things one day at a time.
Were you hoping to reconcile this with her? What were the circumstances of the breakup?
There are very few personal problems that cannot be solved with a suitable application of high explosives.