I think they could have controlled themselves and thrown a tantrum on discord, kept it out of the game, or "silently blocked both". For that matter "loved one"? Are we talking about an internet "gf" who had some "ERP" session? I don't think this equates to "cheating". I mean, are we on the same plane of existence here? The GM was completely right in this. The game is definitely not the place for a personal dispute.