How do the three couples and the concept of love itself function thematically within Othello?

In Othello, Shakespeare presents the
audience with three couples' relationships: Othello - Desdemona; Iago - Emilia; and
Cassio - Bianca. The relationships not only affect the outcome of the plot of the play,
but are intertwined thematically. In each relationship, women are seen to be the victims
of the men they love. Both Desdemona and Emilia die at their husbands'
hands.

Othello and Desdemona's love is sincere and tender,
but vulnerable to the cruel machinations of Iago. Their courtship was brief, and based
mainly on story-telling: 'she loved me for the dangers I had passed/ And I loved her
that she did pity them.' With his limited experience of life beyond warfare, Othello is
unable to counter the insinuations of Iago about Venetian women with his own intuitive
faith in Desdemona's fidelity. He is tortured by gross and nightmarish images of her
supposed sexual liaisons with Cassio, and condemns her as a whore, striking her in
public, and finally smothering her in their bed, lest she 'betray more men'. Desdemona
dies refusing to condemn her hisband; when asked who did the deed, she answers 'I
myself'.

Emilia's feelings for Iago have much more
world-weary cynicism than Desdemona's for Othello (look at her observations in the
Willow Scene), but he means enough to her for her to take the fateful decision to pick
up Desdemona's  handkerchief on Iago's say-so. She doesn't know why he wants it, but no
matter: 'I nothing but to please his fancy.' When, in the final scene, she learns of
Iago's treachery, her determination to reveal the truth costs her her
life.

Bianca, a courtesan, loves Cassio, but he treats her
callously, mocking her devotion in conversation with Iago. He continues the relationship
for his own pleasure, caring little for her feelings, and unwittingly provides 'proof'
of Desdemona's infidelity through iago's orchestration of the eavesdropping scene in Act
4. In Act 5, she is again a victim of male treachery, as Iago pins the blame for
Cassio's injury on her, leading to her being abused and condemned as a whore by all
around her, including Emilia.

Iago is at the centre of all
three relationships; his role is akin to that of a devilish puppet-master. His own
attitude to love is neatly summed up in conversation with Roderigo in Act 1- as far as
he's concerned, it is an illusion: 'merely a lust of the blood and a permission of the
will.'