Archetypical

The biggest threat to lasting mutual satisfaction is the envy of her bitter friend sniping from afar. She announces herself loud, sarcastic and ugly, her joy comes from exercising an instinct for destruction, with subtle and overt suggestions aimed in your young love's ear to wreck relationships under the banner of anarchic freedom.

That this friend has never had a good relationship goes unconsidered, and the costs of her dramatic solutions are not seen until later, too late, her venom performing as designed before what she is becomes apparent.

Just as you must size up and engage a girl's friends when you first meet her, so too in a relationship must you survey and inspect the full set of her friends and their qualities. One of them might be a broken soul unable to resist spreading her vicious malice.