tranquil mind; farewell content;
Farewell the plumed troops, and the big wars.
That makes ambition virtue. O farewell.

When Othello thinks about what he believes is Desdemona's unfaithfulness, he compares her body to his own, showing how he has internalized racism and is filled with a self-hatred which allows him to believe the woman he loves hates him. He says her soul:

is now begrimed and black
As mine own face

Othello takes the tragic step of killing Desdemona. Not only has he destroyed her innocent life, he has destroyed his own. The world seems so dark and hopeless to him at this point that he feels both the sun and moon should be eclipsed at the same time to plunge the world into an utter darkness that would reflect his mood:

O insupportable! O heavy hour!
Methinks it should be now a huge eclipse
Of sun and moon

Othello's tragic flaw is not believing he is lovable, and this, with a great deal of help from Iago, brings him down.

I would select the following lines from Act II scene i which indicate Othello's joy at his union with Desdemona, and yet his feeling is tinged with the strange foreboding that he will never be this happy in his life again -

If it were now to die,
'Twere now to be most happy; for I fear
My soul hath her content so absolute
That not another comfort like to this
Succeeds in unknown fate.

Secondly I would look at the intense emotion Othello feels when he has been convinced by Iago that Desdemona is unfaithful. In Act III scene iii Othello reveals his devastation in a vivid metaphor-

 I had rather be a toad,
And live upon the vapor of a dungeon,
Than keep a corner in the thing I love
For others' uses. 

By Act IV scene i we see Othello reduced to catilepsy as even his eloquent words fail him and he loses control of both his mind and body -

 It is not words that shakes me thus. Pish! Noses, ears, and
lips. Is't possible? Confess?—Handkerchief?—O devil!

By the end of his life, Othello has reconciled himself to his failings and finally kills the only person he can truly blame for his thoughtless and violent reactions: himself-

Speak of me as I am; nothing extenuate,
Nor set down aught in malice. Then must you speak
Of one that loved not wisely but too well;
Of one not easily jealous, but, being wrought,
Perplex'd in the extreme; of one whose hand,
Like the base Indian, threw a pearl away
Richer than all his tribe;

Here Othello realises his fatal flaw, acknowledges it with dignity, then takes his own life.

A short but tragic quote spoken by Othello from act 2, scene 3 is the following, which underscores a key element of the play's tragedy:

Iago is most honest.

Much of the unfolding tragedy can be pinned to Iago's ability to deceive Othello about the kind of person he really is: maliciously bent on destroying Othello. One of Othello's flaws is how he is blinded and manipulated by this man. By the third act, we as the audience know how completely despicable Iago is—in part because he tells us so—and can only react in helpless horror as Othello is deceived.

Another key point of tragedy is that Othello's awareness of Iago's evil comes too late, after Desdemona is dead. Again, a simple line of anguish communicates Othello's deep distress at his own misinterpretation of events and misplaced trust. In act 5, scene 2, he says of himself:

Oh Fool! Fool! Fool!

. . . must you speak

Of one that loved not wisely, but too well.
Of one not easily jealous, but being wrought,
Perplexed in the extreme. Of one whose hand,
Like the base Indian, threw a pearl away
Richer than all his tribe . . .