In the very first scene, we are introduced to the main protagonist, Iago who in his discussions with Roderigo notes in vivid detail his hatred toward Othello. His situation is not an uncommon one, for even in today's world the jealosy and rage felt by those passed over for promotion has boiled over into headlines. In this we can sympathize with the villian. What we find also in Iago is how this event has sparked a rather sociopathic trait, where he has readily forsworn all alliance to his leader, and to everyone else, it seems. It is almost felt that before these turn of events that Iago could have admired Othello greatly.
Love turns to hatred much easier than indifference.
I don't think that Roderigo, being a gentleman of obvious means, is aware of the true depths of Iagos hatred. For some reason, these two have formed a sort of friendship that is agreeable to both, however slanted it might be. Iago tries his best to keep his hands in Roderigo's wallet, which shows perhaps the shallowness of Iago. I think in some way, Roderigo is aware of this, but for some reason does not explore it. Othellos character is indeed an interesting one.