Is the listener to backbiting obliged to inform the person backbited about what he heard, and does the ruling on repentance from backbiting apply to him by clearing his conscience before the backbited person?

Whoever attends a sitting where backbiting is occurring must defend his brother. If he is unable to do so, he must leave the sitting. If he does not do that, he must repent. He is not required to seek forgiveness from the person who was backbited, because he did not engage in the backbiting himself.