STOP! Breathe! Don't do anything. What if your "friend" isn't telling the truth, then you do something mean to David, then he doesn't like you. I never take the word of someone who I know has lied in the past to be the truth. Did she say who the girl was? Could you ask that girl- real casual like, "So, I hear you and David are going out." Or even ask David, you guys are friends, right? Just say to him tomorrow, "I heard that you and so and so are going out now." If he says yes, say, "Oh, she's a nice girl," or something like that. Or he could say, "Why do you care?" or he could say, "No, where'd you hear that?" Either way, it's an opportunity to talk to him, and figure out what's going on.
Jo
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