@Anraex23:
She is definitely tipping off the girlfriend, either because she
intends to steal the guy for herself, or (more likely) because
she takes wicked pleasure in breaking up relationships.

@H-Connoisseur Yeah, the second possibility is more likely esp. considering she insulted him for his forceful technique. IRL there are chicks who go thru scummy lengths to show their friend how "worthless" their friend's boyfriend is. It seems like she could be one of them. [Addition/correction: The only reason why I posted she went to "scummy lengths" is that from personal experience, there are females that have thought or expressed to their best friend that the boyfriend isn't "man" enough or social status acceptable for the girlfriend to have. Since the probable friend got him to cheat, that isn't one of those criticisms and the one time that her concern may be valid.]

@dwellings:
I tip my hat to a sharp-eyed reader.