Othello: The Character of Iago

I knew Iago was the antagonist of the story, so I expected him to clash with Othello and possibly with some of the other characters. However, I never expected Iago to get away with so much. He is constantly lying to various characters and manipulating and turning characters against each other. I thought that some of the characters, especially Othello, would have realized what was going on by now. If Othello gave a promotion to Cassio that Iago wanted, then why would Othello trust Iago the way that he does?
There is so much irony incorporated in Iago's scheming and plotting to take down Othello. Almost every character in the play has said something about Iago being so kind, so nice, and so honest. For example, Cassio says "good night, honest Iago" after Iago has gotten him into so much trouble with Othello (II.iii.300). How could all of these characters have absolutely no idea what is going on around them? Iago's jealousy is what prompts him to do all of these horrible things, yet he warns Othello about the power and destruction of jealousy of other men with Desdemona. "Oh, beware, my lord, of jealousy. It is the green-eyed monster..." I would never be able to be so hypocritical without feeling guilt or anxiety.