I swear, I think my wife is faithful, and I think she's not.
III.iii.197-204 Iago: Watch your wife. Just watch- don't be either completely suspicious or completely trustful. I wouldn't want to see you taken advantage of when you're such a trusting guy.
In this scene, Iago carries out his plan to ruin Othello's life a step further and convinces Othello his wife was cheating on him. This is a person verse person conflict in that Iago threatens Othello's love and relationships, and is also an internal conflict in that Othello believes his truly honest wife to be disloyal, and plans to kill her and Cassio for their "sin." This encounter between the two lovers creates a certain confusion and misunderstanding between the two lovers.
In this scene, Othello believes Desdemona is cheating on him. He argues with her, saying she is a lying whore. This becomes an external person verse person conflict when Othello confronts Desdemona, and the argument becomes physical. This effects the course of the story by creating a barrier between Othello and his wife, and the next stages of Iago's plan to have taken place.
IIII.i.229-232 Othello: I'm glad you're insane enough to admit it in front of me. Desdemona: Why, sweet Othello- Othello: [strikes her] You villain!
III.iii.392-395 Othello: I think my wife is faithful and I think she's not. I think you're trustworthy for one minute and then not the next. I need proof!
When saying this, Othello confesses his confusion and his temptation to take act by either killing Desdemona, Cassio, or himself. This is an internal conflict because Othello does not know what to do or how to react to Iago's lies. It also shows Othello had lost all his love and faith in Desdemona by admitting his will to kill her if it is found she is unfaithful. This effects the plot by erasing all Othello's goodness and heart and reveals his true and new self.