Jealousy repeatedly drives the novel’s characters to make irrational decisions with harsh consequences. This is particularly true of Isabel, though her story is theoretically one of sexual temptation. However, the ruinous mistake at the core of the novel’s conflict is driven by jealousy as much as desire: As the narrator reflects, “[T]here never was a passion in this world, there never will be one, so fantastic, so delusive, so powerful as jealousy” (231).

While she does experience some attraction to Francis, Isabel primarily decides to leave her husband because she is obsessively jealous of Barbara Hare. Isabel’s jealousy toward Barbara, while completely unfounded, is so intense that it becomes obvious to Francis, who exploits this emotion for his own benefit. Isabel’s jealousy becomes a particularly destructive force when it collides with Francis’s relentless self-interest; just before Isabel finally concedes to elope with him, Francis persuades her to “be avenged on that false hound” (322). Isabel will later deeply regret the irrational and reckless decision that entails throwing away her entire life, but she acts under the influence of jealousy.

Jealousy also later drives Isabel to make a second reckless and irrational decision: returning to East Lynne in disguise.