The realisation Othello has of his flaws give the audience a sense of catharsis, the audience feel that now he knows of his mistakes he cannot do more wrong. He feels bad for what he has done and understands that killing himself is the only way to restore order. It is arguable that the play does not give a sense of catharsis because it is never shown that Iago is tortured. The audience never s.
After Iago plants the seeds of jealousy in Othello's mind, Othello complains of having a headache, which is a big, big clue that Othello thinks Desdemona's been unfaithful. In sixteenth century literature (Shakespeare's especially), any time a man has a headache or there's some kind of reference to a man having horns growing out of his head, we can be pretty certain there's a reference being.