You're acting childish, just because she likes your friend it gives you no right to become upset with him or her. She has every right to chose who she wants to be with, no amount of whining or complaining on your part will change that. If you were a real man, you'd be glad she found someone she could be happy with.

And as for your friend, what kind of friend to him are you? It's not betrayal, you didn't do anything with her, you never made your feelings apparent. It's not as if he stole her from you since you never had her in the first place. All you're doing now is keeping him from something that might actually be good.

If she's in love with your best friend then you're done. Don't whine about it, that's just the way it works. It's not going to work and it's not as if you can will it to change so just move on.