Tell me how do I move on?

I definitely understand how you're feeling. I have many friends like that, but one thing you have to remember is that, there probably not just like that with your 'guy'. She probably just likes the rush of being flirty with a new guy. I wouldn't worry. But what you're feeling is jealousy. You don't like him, you definitely have feelings for him though. It might be sympathy for the guy, who thinks he likes this girl, or jealousy of the girl who is stealing your friend away from you. Hanging out with him, just got your feelings confused. Anyone that you don't know for sure, that you like, is probably not the one.