Iago convinces Roderigo that Cassio is in love with Desdemona by manipulating their perceptions and exploiting Roderigo's jealousy. He suggests that Cassio's charm and good looks make him an attractive suitor for Desdemona, thereby fueling Roderigo's insecurities. Iago further stokes Roderigo's desire for Desdemona by falsely portraying Cassio's interactions with her as romantic, reinforcing Roderigo's belief that he must take action to win her back. This deception is a key element of Iago's broader scheme to incite chaos and manipulate those around him.
Roderigo was becoming aware of the fact that the huge sums of money he had given Iago to help seduce Desdemona had been going directly into Iago's retirement fund. When a conman cannot blow off the mark, either he runs or arranges for him to be killed. Actually Iago wanted Cassio to kill Roderigo but he didn't quite do the job so Iago has to finish it.
Iago advises Cassio to ask Desdemona to plead on his behalf. This will help Iago poison Othello's mind, as Desdemona will appear to be doing so out of her (illicit) love for Cassio.
He tells Cassio to ask Desdemona for her help to get him reinstated.
She found a handkerchief, and iago wanted her to copy it.
Iago says that he was sleeping next to Cassio and that Cassio was having a dream about making love to Desdemona.
Iago tells Cassio that he must persuade Othello to reinstate him. He says "the general's wife is now our general" and so the best way to persuade Othello is to get Desdemona to plead on Cassio's behalf. Since Iago has also told Othello that Desdemona and Cassio are having an affair, the harder Desdemona pleads, the worse it is going to look for both her and Cassio.
While Othello is hiding, Iago and Cassio discuss Desdemona. Iago uses this opportunity to manipulate Cassio into speaking favorably about Desdemona, knowing that Othello is eavesdropping. This conversation plays a crucial role in Iago's scheme to incite jealousy in Othello regarding Desdemona's loyalty.
Iago realizes that Cassio greets Desdemona romantically, and with a kiss on the cheek. Supposably that's how you greet the women politely.
Othello was just out of earshot when Iago talks to Cassio. He has told Othello that he is talking to Cassio about Desdemona but he is really talking about the woman that Cassio is really having an affair with, Bianca. In 'Othello' Iago tricks Othello by planting Desdemona's handkerchief in Cassio's room.
Desdemona. Iago says that Desdemona is the most influential person with Othello, so Cassio should get her to plead on his behalf. This sounds reasonable, except that Iago has suggested that Cassio and Desdemona are having an affair, and this will heighten Othello's suspicions.
Iago's master plot to annoy Othello and Desdemona, is to tell Desdemona's father that Desdemona has married the Moor (Othello). And also to convince Othello that Desdemona is involved in an affair with Michael Cassio.
Cassio sees Desdemona as a sort of secular Virgin Mary, as from the quote, "O behold...Hail to thee lady!". On the other hand, Iago sees Desdemona as competition for Othello's affections.