I'll always care for you, and you know that. I wish it were different.
The Apple of Discord is a reference to the Golden Apple of Discord, which, according to Greek mythology, the goddess Eris, inscribed "To The Fairest" and tossed in the midst of the festivities at the wedding of Peleus and Thetis, thus sparking a vanity-fueled dispute between Hera, Athena and Aphrodite, that eventually led to the Trojan War.
Thus, "Apple of Discord" became a euphemism for the core, kernel, or crux of an argument, or for a small matter that could lead to a bigger dispute.
Because of this, the Roman goddess corresponding to the Greek Eris was named "Discordia".
