"Cassio, my lord? No, sure I cannot think it That he would steal away so guilty-like, Seeing you coming."
Iago's interpretation of Cassio's exit, combined with Desdemona's vigorous support on Cassio's behalf, creates suspicion in Othello's mind even before Iago prompts him. Othello manifests his confusion about his wife by telling her that he wishes to be left alone, and by rejecting her offer of help when he tells her that he feels unwell:
"Your napkin is too little. Let it alone."
When Desdemona advocates on Cassio's behalf, she initiates the first real conversation she has had with her husband throughout the play. She also displays her strong, generous, and independent personality. In addition to his burgeoning suspicion, Othello's moodiness may also result from his dislike of Desdemona herself. Only once Desdemona has left does Othello recover somewhat: "Excellent wretch!" he says affectionately. "Perdition catch my soul, But I do love thee, and when I love thee not, Chaos is come again".
Othello seems far more comfortable expressing his love for Desdemona when she is absent. Perhaps this is because her presence makes him conscious of her claim upon him and of his obligation to honour her requests, or perhaps this is because he is more in love with some idea or image of Desdemona than he is with Desdemona herself. The lines just quoted indicate how much his image of her means to him: if he stops loving her, the entire universe stops making sense for him, and the world is reduced to "chaos."
Given how much is at stake for