I'm really curious as to why this girl has some weird obsession with the other guy when she's banging you. Why is she trying to make HIM jealous, knowing that no good can come of it for YOU?
My take is that she has some sort of history with the other guy--maybe she liked him at one time and he coolly rejected her and now wants her, maybe it was more serious than that. It's not normal for an AW to single out a random guy like that, unless he's guilty of a lot more than just liking her.
Anyway, you told her if she pulled that nonsense again you were done, now hold your position. I would tell her to block this guy's # and cease contact with him, just to test how serious she is about you. This is really the only way this drama isn't going to resurface. Be sure she knows it's not about trying to control her or who she talks to, it's about the fact that this other guy is trying to sabotage your relationship (or "whatever"-ship) and WILL break the two of you up if she continues to let him harass her.
WATCH OUT FOR AFC ORBITERS!! They may seem harmless, but they can stir up all sorts of drama and destroy your relationships. If a guy makes his interest known to your girlfriend, it is her responsibility to cut contact with him, outside of a work environment. There is ABSOLUTELY NO GOOD that can come of having an AFC constantly trying to wear down your girlfriend.