eris the goddess of discord wasn't invited to tea, so she threw an apple on the table in front of aphrodite, hera and athena addressed "to the most fair." those three started arguing about it, then went and got a mortal, paris of troy, to pick one of them. athena promised paris great wisdom if he picked her; hera great power; and aphrodite promised him helen, the most beautiful woman in the world.
this was no affair. it happened because of the gods.
and while we're at it, Patroclus did definitely NOT nick Achilles' armour and FOOL his Myrmidons into following him to battle. Patroclus BEGGED Achilles to intervene and then compromised to don his armour & lead his troops when Achilles wouldn't (over the slavegirl).