3x16 "The One with the Morning After"

Ross wakes up the next morning full of regret after sleeping with Chloe, and is forced to hide her when Rachel visits him hoping to make up. Although he is initially successful, he is exposed when the secret makes its way to Gunther who doesn't hesitate in telling Rachel everything. The two go back to her apartment and have a huge fight, as the other four friends are trapped in Monica's bedroom, forced to listen in. The argument lasts for hours, and although Ross is desperate for forgiveness Rachel refuses and ends the relationship completely.