Except it really wasn't. Cleopatra and Antony were two powerful politicians who enjoyed one anothers company on occasion. But they also didn't see one another for years on end. They had two children that were illegitimate in *both* of their cultures together, sure. But their alliance was mainly one of political strength and convenience.
Anyway. I found this little aside about Roman sexual mores interesting:
"The Romans took an unsentimental view of sexual relations. Romantic love, as we know it, was rare. Public displays of affection were frowned on, as was excessive sexual activity. Marcus Porcius Cato the Censor, who lived in the second century B.C., set the standard for conventional good behavior when he expelled a man from the Senate for kissing his wife in the street.
"A Roman man, almost invariably locked into a marriage of convenience (although second or later unions often permitted a freer choice), did not suffer feelings of moral guilt about sex, nor did he feel necessarily bound to any particular sexual object. He would not have understood modern terms such as 'heterosexuality' or 'homosexuality,' which categorize people as sexual types. What he did was the issue, not what he was.
"To judge by literary sources, it did not greatly matter whether the randy husband fancied a young man or woman. The poet Horace was not untypical of his age:
When your organ is stiff, and a servant girl
Or a young boy from the household is near at hand and you know
You can make an immediate assault, would you sooner burst with tension?
Not me. I like sex to be there and easy to get.
"According to Suetonius, Horace had his bedroom lined with mirrors; he brought hookers or rent boys there and enhanced his pleasure by turning his own sexual experience into pornographic imagery.
"Two chief concerns governed sexual conduct. First, a free male citizen should be the one who performed the penetrative or insertive act, who was the 'active' rather than the 'passive' partner. For him to be sodomized was shameful, a betrayal of his masculinity. Anyone who was known to enjoy being buggered was scorned. This was why Julius Caesar deeply resented the story that in his youth he had been the catamite of the king of Bithya, and the gibe of a political opponent that he was 'every woman's man and every man's woman.'
"Second, an adulterer or fornicator was meant to restrict his attentions to noncitizens and slaves, as in Horace's case; freeborn boys and women were out of bounds. Although there is plenty of evidence that this was a custom honored mostly in the breach, it was essential that there should be no doubt as to the identity of a Roman citizen's father. This was why Octavian ordered a favorite freedman of his to commit suicide after he had been convicted of adultery with Roman matrons. In addition, foreign genes should not be permitted to enter the Roman gene pool; only citizens could marry citizens, and to wed a foreigner was frowned on; if not illegal, such a union was unrecognized by the law, especially when it came to acknowledging heirs in a will.
"What all this signified as far as Antony was concerned was straight-forward: he could not marry Cleopatra, who was as non-Roman as they came, but if he wanted to conduct an affair with her it would be odd if anyone complained. Roman women, such as Octavia, well understood the conventions; her husband's extramarital dallying did not strain her loyalty to him. It was her brother who could not stand the idea of her betrayal by Antony's entanglement with an eastern temptress." - p. 149 - 150
In case you didn't know, Antony married Octavian's sister, Octavia, in a bid to cement the two families together and stop some of the fighting. It only worked marginally. Antony and Octavian were rivals forced to work together until all their other enemies and rivals were gone. Then they would turn on one another.
Also, Octavian couldn't let Cleopatra and Antony join forces, or at least not for long. Cleopatra, after all, was the mother of a blood child of Caesar's. Caesarion. While illegitimate, since his father had been declared a god, Caesarion represented an untenable threat that would have to be removed. Let's keep in mind that Caesarion, at this point, was only 11. But he was already technically co-monarch of Egypt, with his mother.
You can probably guess, from the way history talks about Augustus and *not* Caesarion, that this story does not end well for Caesarion.