If Othello had a tragic flaw, it would be jealousy or pride. He is more concerned with posessing Desdemona than loving her. Essentially, he was jealous because of his pride.
The flaw that Iago plays on so ruthlessly, and the one that ultimately causes Othello's fall, and Desdemona's death, is jealousy. Othello is so blind with rage at the thought that his wife might have been unfaithful to him that he is incapable of listening to reason. He is particularly susceptible to Iago's machinations because he of a different race, and perhaps already feels like an outsider, and as important, because he is much older than his beautiful wife.He murders his wife from rage born of pure jealousy.