Othello's tragic flaw is his jealousy, which ultimately leads to his downfall. He is consumed by suspicion and mistrust, and this blinds him to the truth. Throughout the play, Othello becomes increasingly jealous of his wife, Desdemona, whom he believes is having an affair with Cassio.
One of the most prominent examples of Othello's jealousy is when Iago convinces him that Desdemona is unfaithful. Othello becomes so convinced that he decides to kill her. He says, "I'll not expostulate with her, lest her body and beauty unprovide my mind again. This night, Iago. Do it not with poison, strangle her in her bed, even the bed she hath contaminated."
Othello's jealousy also causes him to doubt the loyalty of his closest friend, Cassio. When Cassio is involved in a drunken brawl, Othello believes that he is unfit for his job and dismisses him from his post as lieutenant. This decision ultimately leads to Cassio's involvement in Iago's plot against Othello.
In addition to his jealousy, Othello's other tragic flaw is his inability to control his emotions. He is quick to anger and acts impulsively, which leads to his downfall. He is also too trusting of others, particularly Iago, which allows Iago to manipulate him.
In the end, Othello's tragic flaw of jealousy and his inability to control his emotions lead him to murder Desdemona and then take his own life. The play highlights the dangers of jealousy and the consequences of giving in to one's emotions.