Faith, he to-night hath boarded a land carack:
  If it prove lawful prize, he’s made for ever.

In act one scene two, Iago proclaims to Cassio that Othello has eloped with Desdemona. Apart from the materialism and chauvinism Iago showcases in his speech, he reveals his intention to psychologically isolate Cassio.

It is later revealed in the play that Othello was much closer to Cassio than he is to Iago. Cassio accompanied Othello on his journeys to woo Desdemona and played a significant role as a matchmaker in Othello’s love story. Even so, Othello abandoned Cassio when he made Desdemona elope with him.

Apart from that, the words of Iago indicate how he makes sure Cassio acknowledges the fact that he has been isolated by his friend, Othello.