To question Othello's actions when a man "not one easily jealous" kills his wife on circumstantial evidence and hearsay, is most reasonable. It seems that Othello was equally and overly, trusting and never wondered about Iago as he was, after all, "honest, honest Iago." One of Othello's most endearing and most frustrating character traits is his belief in the absolute - absolute love, absolute trust, absolute perfection (in Desdemona).
Othello should have been aware that it would have been basically impossible for Desdemona and Cassio to be together "a thousand times." Othello is a general, he leads, he strategises, he makes life-changing decisions in battle. Surely then, he should also have recognized Iago's dissent and his frustration at having been passed over in favor of Cassio and that he served Othello only to "serve my turn upon him."
However, Othello is a complex character who may not be easily aroused but, once he is, he is irrational. He does not know the way of European women; he lacks sophistication; he sometimes feels he must prove himself. When he tells Desdemona's father that he did not "bewitch" his daughter and that she truly loves him, -"she had eyes and chose me"- he is convincing himself as much as anyone else. Ultimately he believes himself to be nothing but a "turban'd Turk." Othello internalizes his fears and creates his own reality.
The "physical" evidence that convinces Othello is the handkerchief. "That handkerchief which I so loved and gave thee, " becomes the "ocular proof" he has been seeking. Even when Desdemona expresses her surprise that Cassio has her handkerchief, Othello is too obsessed with the appearance of infidelity and thinks she is just lying to him. So crazed is Othello that he will kill Desdemona so that "I can again thy former light restore." He wants to restore her to the perfect being she was when he first met her. The fact that Othello thinks that he can save Desdemona from herself by killing her adds to the recognition of Othello as a "tragic hero" with a fatal flaw.