Why would I think you're obsessed with this girl if you post on the internet bashing her to a bunch of strangers, divulging how two of your friends have had her, how you alternate between pretending to be her friend and then completely ignoring her, and how your girlfriend will shun friends if they dare speak to her in public? Then you expect us to believe you're the victim here? Yeah, it's beyond me to imagine why the problem might be on your and your friends' side of the aisle.
In my experience, the ones who cry for a reprieve of drama are the ones who cause the most drama. Your depiction of your situation isn't qualifying as an exception to that rule.
Just leave her alone. Stop talking about it. Just leave her alone. I know this is all high school drama llama junk but, seriously, just leave her alone. This means you don't talk to her, you don't hang out with her, you don't have prolonged explanations why you don't talk or hang out with her, you don't talk about her amongst yourselves, you don't post on the internet about her, you don't shun people who talk to her, and you all stop taking turns sleeping with her. Just leave her alone.