Aristides (2.2-2.3)

and that by this very rivalry their natures were straightway made manifest, the one as dexterous, reckless, and unscrupulous, easily carried with impetuosity into any and every undertaking; the other as established on a firm character, intent on justice, and admitting no falsity or vulgarity or deceit, not even in any sport whatsoever. But Ariston of Ceos says that this enmity of theirs, which came to be so intense, had its origin in a love affair.

They were both enamored of Stesilaus, who was of Ceian birth, and in beauty of person the most brilliant of youths; and they cherished their passion so immoderately, that not even after the boy’s beauty had faded did they lay aside their rivalry, but, as though they had merely taken preliminary practice and exercise in that, they presently engaged in matters of state also with passionate heat and opposing desires.