Aemilia Lepida

This Aemilia was daughter of Mamercus Aemilius Lepidus Livianus, wife of Metellus Scipio and former fiancee of Cato. Her daughter was Cornelia Metella, last wife and widow of Pompey the Great. Although Aemilia Lepida was engaged to be married to Cato the Younger, she in fact married someone else, leaving Cato to marry Atilia. In the words of Plutarch's Parallel Lives, Life of Cato the Younger, 7:

When he thought that he was old enough to marry,— and up to that time he had consorted with no woman,— he engaged himself to Lepida, who had formerly been betrothed to Metellus Scipio, but was now free, since Scipio had rejected her and the betrothal had been broken. However, before the marriage Scipio changed his mind again, and by dint of every effort got the maid. Cato was greatly exasperated and inflamed by this, and attempted to go to law about it; but his friends prevented this, and so, in his rage and youthful fervour, he betook himself to iambic verse, and heaped much scornful abuse upon Scipio, adopting the bitter tone of Archilochus, but avoiding his license and puerility. Lepida and Cato were first cousins with Lepida's father and Cato's mother being blood siblings.

Source :

https://en.wikipedia.org/wiki/Aemilia_Lepida