I think you should think what you did to her. Did you talk with her as you used to? Did you comfort her whenever she meets some trouble? Did you give her a shoulder whenever she want to cry? Did you know what she feels about the family about you about herself? It is easy to find the help from the net if she can't get the help from nearby.
But if you already lost her and nothing would turn her back, just don't fool yourself and leave her. I know it is easy to say than to do. But that is the only thing you can do. Don't hurt yourself any more and let her free.