Okay, in hindsight, I think I get what got to Harsen.
"You were my best choice."
Hearing that over and over again, it's basically like being told that they were picked to settle on and that there is nothing about the person themselves to like, just their position.
Ercella is basically always telling him that she doesn't care about him, just his status.
In other words, they need someone to mediate between them. But couples counseling does not exist.