To consider the outcome and unfortunate end of the main characters in Othello, it is important to look at the themes, especially Othello's jealousy. All the characters have flaws; Desdemona is too trusting, Iago is too manipulative; Othello is too trusting but in a far more selective manner. His trust in "honest, honest" Iago is completely misfounded and his lack of trust in Desdemona brings this play to its disastrous conclusion.
Appearances are deceiving and, none more so than in Othello. There is a need for the characters to question each other's motives but all Othello needs is "ocular proof" and the flimsy handkerchief is enough for him. We know that Iago will "pour this pestilence into his ear" (II.iii.351)and Othello is so affected by his belief in the esteemed worth of the military (and by default Iago) that, even when Desdemona claims innocence "Let him confess a truth" (V.ii.70) Othello still kills her because she "was as false as water." (137)Even when he realises his error and that Iago is a "demi-devil" who "ensnared my soul and body"(304-5), Othello still considers himself an "honorable murderer (297).
Perhaps Desdemona does not have the life experience to recognize her own contribution to her husband's rising jealousy. She is however his wife so, especially in Shakespeare's day when expectations within a marriage would have been quite different from today, she should have been mindful of appearances. A woman befriending a man would often be frowned upon. Desdemona however knows Othello is not jealous - at first - so proceeds naively with her relationship, walking straight into Iago's trap. It is inconceivable to her that "there be women do abuse their husbands"(IV.iii.60).
Iago a self-confessed manipulator, proud of the fact that "I am not what I am" (I.i.65) extends the theme of appearances but is also a victim of his own schemes. He is so arrogant as he watches his plan come together that even when Othello wounds him, he still believes he is invincible "I bleed, sir; but not kill'd."(V.ii.292)