Men get over it, she does not like you.
I suspect your friend doesn't even like her, maybe because he knows you like her.
Chat to your friend ask him if he likes her.
If he does, give him you blessing and let them hook up, if he doesn't tell her not to waste her time and YOU back off. Don't even think about her, move on to other women.
Think of the saying "absence makes the heart grow fonder" if its meant to be you and her then hey, if not hey again but DONT hold you breath on it.
But in all probability they is nothing you can do other than back off and start meeting other women. Plus if you think about it, as a guy, do you really want to go out with someone who doesn't like you?