Why is Roderigo angry with lago?

Iago is aware thatDesdemona, the daughter of Brabantio, a Venetian nobleman of some stature, has run off with Othello, the black warrior of the Moors. Brabantio knows nothing of this coupling; Iago decides to enlist Roderigo, who lusts after Desdemona, to awaken Brabantio with screams that his daughter is gone. Roderigo is angry that the woman he desires has been intimate (married) to the Moor.