Is't lost? Is't gone? Speak, is't out o' th' way?
I marry her!What?A customer?Prithee bear some charity to my wit.(IV.i.116-117)
DO YE TRIUMPH,ROMAN? DO YOU TRIUMPH!!!(IV.i.115)
She gives it out that you shall marry her. Do you intend it?(IV.i113-114)
Othello accuses Desdemona of cheating with Cassio, because of Iago's lies. Iago sarcastically mentions to Othello to watch how Desdemona is around Cassio. However, Othello doesn't believe him without proof. Desdemona loses her handkerchief and Emilia finds it and gives it to Iago. Iago places the handkerchief in Cassio's room, so it would appear as if Desdemona gave it to him. Othello questioned Desdemona of where her handkerchief was, she couldn't reply. This is an external person v person conflict for Othello. He now thinks that Desdemona is untrustworthy and cheated on him.
This scene shows an internal person vs self-conflict for Othello.Iago orders Othello to hide nearby and observe Cassio’s face during their conversation. Iago explains that he will make Cassio retell the story of where, when, how, and how often he has slept with Desdemona, and when he intends to do so again. The readers then are informed about Iago's intentions. He will joke with Cassio about the prostitute Bianca so that Cassio will laugh as he tells the story of Bianca’s pursuit of him. Othello will be driven mad, thinking that Cassio is joking with Iago about Desdemona. The plan works. After being lied and manipulated to by Iago, Othello is questioning Desdemona's loyalty aAfter it is revealed that Cassio had the handkerchief that he gave as a present for Desdemona, he makes plans to kill both of them, which is a hard decision.
In this scene, Desdemona enters with Lodovico, who has come from Venice with a message from the duke. Lodovico irritates Othello by inquiring about Cassio, and Desdemona irritates Othello by answering Lodovico’s inquiries. The contents of the letter also upset Othello—he has been called back to Venice, with orders to leave Cassio as his replacement in Cyprus. When Desdemona hears the news that she will be leaving Cyprus, she expresses her happiness, then Othello strikes her. Lodovico is horrified by Othello’s loss of self-control Lodovico cannot believe that the Othello he has just seen is the same self-controlled man he once knew. This is an external person v society for Othello. His actions ruined his reputation as a general.