In the Nyantcha continuity did Aether and Amber ever have an actual thing?
No not exactly. Aether went to Amber's house with some flowers, presumably in an attempt to woo her, but instead he stumbled on a topless and sweaty Kaeya answering the door, while Amber was laying on a table in the back limp as a noodle after a presumably raunchy session. And then Nyantcha drew more Kaeya X Amber art showing that they continued their highly sexual relationship after that incident.