In Act 3 Scene 3, how is Othello manipulated by Iago?

Othello "divorces" Desdemona in this scene and effectively "marries" Iago by the end of it.

Iago's web of treachery has taken over three of Othello's "senses": hearing, sight, and language.  Like Oedipus, Othello is deaf, dumb, and blind to the truth.

First, Iago appeals to Othello's ear by planting how Desdemona and Cassio have be cheating on him behind his back.  This riles Othello's jealousy, and the "green-eyed monster" takes over Othello's emotions, limiting his use of reason and language.

Next, Iago gives Othello "ocular proof" of Desdemona's betrayal by linking the handkerchief with Cassio.  The handkerchief, once a symbol of Desdemona's love, now becomes one of betrayal.  Iago has managed to let everyone get their hands on the handkerchief; it goes from Othello to Desdemona to Emilia to Iago to Cassio to Biancha.  It travels from a virgin to a "whore."  When Biancha brings in the magic hanky, Othello resolves to kill both Cassio and Desdemona.

Finally, Iago reduces Othello to a trance-induced "horned beast" who utters monosyllabic nonsense.  The once-mighty Othello of Act I, who argued so well against Brabantio, who used words instead of violence, whose speech was filled with wondrous pathos, now sounds like Brabantio from Act I:

Damn her, lewd minx! O, damn her!

O, blood, blood, blood!

I'll tear her all to pieces.

O monstrous! monstrous!

Iago proves that he who controls language controls people.  Iago has Othello by the strings, and he schemes to have his puppet strangle Desdemona in bed, which should be reserved for eros (physical love); instead, it will be a place of theros (death).