Hmmm...Ok , I personally think you?ve done the right thing so far, you?ve told her how you feel, but could she have misread the statement love as in platonic love not romantic love, verify the fact that she understood what you meant, what you said and you are serious about it.
Now the second problem is her ex, I personally don?t think his feelings towards her should matter to you, as people we?re entitled to our individual emotions, as long as they don?t violate or impose on a third or a second party, I guess what I?m trying to say is you shouldn?t give a rat?s behind about how he feels, your feelings are as equally important.
Finally you need to realise that, you cannot make someone fall in love with you by force or by manipulation; as you grow older you?ll understand, that feelings created through force only lasts as long as the force it self lasts. What I?m trying to say is that ultimately no matter what you or her ex does it?s up to her who she wants to love, and the right that you have to love her applies to her as well, she has the right to love who ever she chooses.
I say go to the party enjoy your self, maybe some thing will come of it, maybe it want, my friend you?re just 16 life is just beginning, if it doesn?t work don?t get yourself down there?s always hope and opportunity.