So what does that mean? This game was still being played last week. I still lost it because of this. Unsatisfying response, they've been at it for a long time.

They pretty much couldn't be more obvious. There was a long uncontested border between them throughout the whole game.
Then I looked into it and they play together an awful lot and, surprise surprise, have the same exact responses when other players accuse them of secret diplomacy.

They're ...

"please add me"or something similar