Walt makes a valid and good point but.... Female friend code should automatically point the friend off of him. (Unless he is like the only boy for miles around and you two are the only girls left on the planet....)
I like this guy that ended up having feelings for my best friend. She knows that I am pretty upset about it. Is this something she should pursue or as my best friend should back off?
If they like each other, they should pursue it.
You don't own a "right" to him.
You didn't ask him out, even.
He has decided who he likes. If your friend likes him back, then they should pursue it. I understand you are hurt, but sometimes life hurts. Your feelings should not overshadow anyone else's chance for happiness. Especially if you are truly a friend. With that said, your friend whom I presume knows how you feel, should pursue it is a discrete way and not be doing so constantly in front of you.
Friends don't work that way, if she was truly your best friend you wouldn't even think of asking her to back off, you'd be happy for her, but obviously instead of being happy for her you're having a jealous hissy fit because he wasn't into you.
