Concubinage in Rome was actually not recognized except for unmarried folk, and then concubinage was still a (legally) monogamous contract that did not acknowledge one man with multiple concubines, while a man sleeping with his male friends would have been frowned upon - because a friendship is founded between equals, while Romans saw sexual penetration as inherently involving the domination of one party over the other. Sleep with actors and male prostitutes, like a decent citizen!
I mean, orgies predate Rome.
Concubinage in Rome was actually not recognized except for unmarried folk, and then concubinage was still a (legally) monogamous contract that did not acknowledge one man with multiple concubines, while a man sleeping with his male friends would have been frowned upon - because a friendship is founded between equals, while Romans saw sexual penetration as inherently involving the domination of one party over the other. Sleep with actors and male prostitutes, like a decent citizen!