Me and my friend are fighting over a guy, what should I do?

This guy is telling me one thing and telling my friend another. I know they were spending time with each other first and she knew him first but i thought it was a friendly way. I didn't know she liked him. When she wasn't there, he initiated everything, he flirted with me and acted as if he liked me. So one day i told my friend about him and telling her how much i like him and we got into an argument because she thinks im jealous of her and thinks im trying to sabotage her relationship. I think its his fault because he doesn't want to talk about it and doesn't like to be anywhere where me and her are going to be there at the same time.
Me and my friend are fighting over a guy, what should I do?
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