Of all the passions, jealousy is that which exacts the hardest service, and pays the bitterest wages. Its service is to watch the success of one's enemy; its wages to be sure of it.
Love may exist without jealousy, although this is rare: but jealousy may exist without love, and this is common; for jealousy can feed on that which is bitter no less than on that which is sweet, and is sustained by pride as often as by affection.
Jealousy is sustained as often by pride as by affection.