<human>: Names have been changed to protect identities.

A good friend of mine (Sam) recently told me she was into me, and I had to decline because I was in a relationship. We handled it like adults should and decided to be able to remain good friends despite this event. An anonymous person (just a number we didn't recognize, it wasn't blocked) texted my girlfriend (Beth) while she was at work a few days later and told her "Sam is coming after your boyfriend and you need to watch your back" and other details that could have only been obtained from actually seeing our text conversation.

Beth didn't want me to talk to Sam after this because she was worried about her coming onto me or something. I told her that we handled the situation like adults and I am going to keep my good friend. Days later a horrible post appeared on some defamation website called thedirty.com and a random person Facebook messaged Sam to tell her that she had been posted on it. She discovered the post and immediately blamed Beth, as well as rallied my other friends against Beth for doing such a horrible thing. I confronted Beth about it and was shocked to hear about this posting, and denies that she would ever do such a thing.

Now I am left in the situation to either stick by Beth and losing a group of my close friends and colleagues and tainting my professional reputation, or breaking up with Beth for something she didn't do in order to control collateral damage for all my other relationships.

I think it's pretty clear that the prime suspect is the mystery informant to Beth, but I don't know how I can find out who a person is from their phone number.

Provide a brief overview of the text.
<bot>: Break up with my girlfriend for something she didn't do to not lose everyone else close to me, or stick by her while losing all my close friends and professional colleagues?