Fortunately you've described this to be "just a crush".

Maybe your friend didn't really understand about that it was important to you - although you had said that you could never go after him. Maybe she doesn't realize that you expected the same from her.

But - I ask why are you hurt that she would do this to you? Just because someone "goes after" a guy - doesn't mean that he has obligations to that person (unless he has agreed to some kind of commitment). Same as a girl - if one or more guys goes after her - she doesn't owe herself to any of them.

I apologize if I sound critical in any way - not trying to criticize. Just trying to explain a situation in which there is no commitment.