Iago the antagonist in Othello is the epitome of how jealousy can take over a man and cause him to go to all ends to gain something for what he has lost. In this case his loss of the position of lieutenant to Cassio. At the end of his tale to Roderigo about how he was passed over for promotion to lieutenant, Iago displays his jealousy of Cassio. He says that Cassio, a "counter-caster"(I, i, 31) has the job Iago wanted, while Iago has to keep on being "his Moorship's ancient [ensign]” (I, i, 33). This position is of great value in general and especially to Iago. "I follow him to serve my turn upon him: / We cannot all be masters, nor all masters / cannot be truly follow'd…Wears out his time, much like his master's ass..." (I, i, 40-48). In reality it could have been anyone not just Cassio that could have caused Iago’s green monster to unleash itself to wreak havoc unto Othello.
A more emotional familial level of jealousy, is when Desdemona’s father, Barbantio, is extremely infuriated after losing his daughter to a marriage he did not approve. After Desdemona makes it clear that she loves and respects her husband, Brabantio remains spiteful, and bitterly cautions Othello that Desdemona may turn out to be a whore, "Look to her, Moor, if thou hast eyes to see: / She has deceived her father, and may thee" (I, iii, 292-293). No father has ever expressed a more abhorrent jealousy of his son-in-law. For a father to sabotage his own daughter gives truth of how close love and hate run together in all types of situations not just in love or business.
Othello and Desdemona are head over heels in love with each other in the beginning after getting married despite her father’s opposition it seemed to them they were in the clear after making it through that obstacle. Love and hate run so closely together because they are both feelings of great passion, and jealousy resulting in losing someone of value in this case Desdemona is what pushes Othello across that thin line. “Think'st thou I'ld make a life of jealousy…For she had eyes, and chose me. No, Iago; / I'll see before I doubt; when I doubt, prove…And on the proof, there is no more but this,—/Away at once with love or jealousy!” (III, iii, 176- 192) A.C. Bradley