The ancient Thebans never forced their armies to put up with “don’t ask, don’t tell.” Instead, they created the Sacred Band of Thebes*, an elite force of 150 pairs of lovers – each couple had an older heniochoi and a younger paraibatai – with the idea that soldiers would fight harder and better if fighting alongside a lover. The system was instituted by the commander Gorgidas in 378 B.C. Initially, members of the band were dispersed throughout the ranks of the army, but the general Pelopidas had them fight alongside each other.
The end of the Sacred Band came at the hand of Philip II of Macedonia at the battle of Chaeronea in 338 B.C. When the rest of the army turned and fled from Philip’s better-armed forces, the 300 remained and fought to the death. In about 300 B.C., Thebes erected a statue of a lion on a pedestal over the grave, a monument that still stands today. An excavation of the site turned up 254 skeletons, meaning most likely that not all of the Sacred Band were killed.
Plutarch reports that when Philip came upon the corpses heaped together after the battle, he said: “Perish any man who suspects that these men either did or suffered anything unseemly.”
There is a wikipedia page for Sacred Band of Thebes here.
* Plutarch gives a convoluted explanation as to why the force was called sacred: “It is a tradition likewise that Iolaus, who assisted Hercules in his labours and fought at his side, was beloved of him; and Aristotle observes that, even in his time, lovers plighted their faith at Iolaus’s tomb.” You can read more of Dryden’s translation of Plutarch here. On another note, the campy Swedish pop band Army of Lovers is named for the Sacred Band of Thebes.