in iagos closing soliloquy in this scene he provides another reason for his plan to torment othello what is this reason

Though Iago seems grieved by Cassio's promotion over him, this does not seem to be his main, or only, motive. Iago mentions the promotion to Roderigo, to convince him that he hates Othello; but Iago also cites his suspicions that Emilia and Othello have had an affair as another reason for his enmity.