Nahh he's on heinley's side and he has some personal grudge ヾ(❀╹◡╹)ﾉ~
I haven't read the novel, so I can't say for sure. But it honestly looks to me that he's playing a long con for Heinley, but like at his own discretion. They're obviously friends, and nothing he's doing is against Heinley, not really. And everything he's doing for Rashta, there's always at least one point where things will go wrong eventually, and all of it will poison her relationship with Sove. Like the dude said he liked Rashta for her "innocence" but she's been actively and intentionally manipulative and malicious which will probably become obvious to the emperor after its too late and the empress remarried. I think that advice Ergi just gave in ch. 71 of acting like the fake nobles are her parents will clue Sove in on how good of an actress Rashta is, so what else could she be faking?
I really can't tell if Ergi is trying to help or not. Cause on one hand, he is speeding up the divorce and covering for Mckenna, but he's also helping the filthy piece of trash and I can't tell if he's doing it to harm her(Trashta) later by revealing the truth or just playing both sides.
I still like him though! (づ￣ ³￣)づ