how did the relationships in Shakespeare's Othello contribute to the tragic ending?

Othello is a slave to his passions. He sees things in absolutes and Iago knows this and exploits it.In matters of military, Othello can be subtle and wise. In matters of the heart Othello is rash and judgmental. It couldn't have been easy being a "moor" in Shakespeare's world at that time. Othello is defensive when it comes to how he is scene in society, especially when it comes to matters of sex marriage, and emotional stability. Othello's judgment in these matters is easily clouded with the slightest doubt. This doubt/ lack of control snowballs quickly into paranoia and violence. Othello's rash emotional judgement leads to his killing of Desdemona. Emilia unwittingly does Iago's bidding. Being subservient to her husband, she plants the scarf that will undo Desdemona. Iago is a master of manipulation and, although Emilia stands up to him in the end, she does what is expected of her. Much like Emilia, Bianca unwittingly functions to call Michael Cassio's credibility into question. This of course is all masterminded by the evil Iago.