I cry you mercy then. I took you for that cunning whore of Venice That married with Othello.—You, mistress,
At this point, it looks as though Iago's manipulative behavior is no longer needed because Othello is internalizing the lies and believes them at this point. He has fully submerged himself in the lies that come out of Iago's mouth that he deems true. He doesn't even sound like himself, calling Desdemona a "cunning whore of Venice".