Motives of Iago

"Demand me nothing. What you know, you know. From this time forth I never will speak word (V, ii, 302-303)

This is all Iago leaves is with. No last explanation or spiteful words. Truthfully, I have no idea what Iago's motives were and will not pretend to know; but, all I can do is offer up possibilities. One theory I have depends on Iago's state of life. Obviously this was a man in an awful marriage, not where he wanted to be professionally, and possibly in a life he thought was meaningless. Being a little demented, he might have just had no hope in life and wanted to go out with a bang and be remembered. While that theory may be far-fetched, this one might be more plausible. What took down Othello? Jealousy. Multiple times in the story Iago speaks highly of Desdemona, which he often doesn't do for women. This leads me to believe he wanted Desdemona to himself, but knew how unrealistic it was. In order to right this wrong, he decides to take down Othello with the green-eyed monster that consumes him: jealousy. Either way, it seems obvious to me that Shakespeare is commenting on how much love can change, consume, and distort the minds of even the best and brightest. I'm reminded of the movie Hancock in which immortals are paired together at the creation of the universe and only become mortal and powerless when they get close to their eternal partner. All humans, even the great Othello, are weak to Cupid's arrows.