In Greek mythology, Cometes (Ancient Greek Κομήτης) son of Sthenelus is the lover of Aegialia, wife of Diomedes, while the king fights at Troy. Apollodorus' Epitome has Nauplius' intrigue, the barred gates at Argos, and Diomedes' night withdrawal into exile when he cannot punish the adulterer.
Adapted from Wikipedia, "Cometes" · CC BY-SA 4.0
I.Adulterer of the Returns
Apollodorus (Epitome 6.9–10) says Nauplius contrived that the victors' wives play them false: Aegialia took Cometes son of Sthenelus as lover. When Diomedes put in at Argos with Trojan spoils, the city was closed against him; protected by Aegialia's favour and Argive numbers, Cometes could not be punished without civil war, and Diomedes withdrew by night into exile.
Wikipedia also lists a Peirasian father of the Argonaut Asterius, a Lapith at Pirithous' wedding, a brother of Althaea, and a son of Tisamenus — none is this Argive adulterer.
II.Homonym care
The atlas id cometes-argolis is Sthenelus' son in the Diomedes–Aegialia Returns story alone. Do not merge with Cometes father of Asterius in Apollodorus' Argonaut catalogue.