Ouch, that stings. I think if she was your true friend, she would believe you. Obviously she's known you longer, right? Maybe you should try talking to the guy and ask him why he's spreading stuff about you talking trash. But if he doesn't listen, just ignore him. And try not to beg for your friend back.. it gives her power to control you. and say, "aha.. no!" And then you'll get in a bad mood, and she'll keep doing it. or at least, that's what usually happens.