I could ask you the same question. Politics don't work like that. You need allies and Etienne needs both to take de throne as smoothly as possible, his father's and mother's. Rishar doesn't care about this and that is sadly a liability in this context. Etienne is bad at judging character but he IS more rational at decision making, even after being isolated for so long
Oh, I see you lack both comprehension and empathy. Children who are abused often still crave love from their abuser. I’m studying psychology, and what he’s showing are classic signs of what’s called a trauma bond, especially in cases involving family abuse. He wants to be loved by both of his parents, but he received neither love nor acknowledgment. It’s a very complicated situation because victims often struggle to let go of the person who abused them. I hope you don’t use degrading words toward someone when you don’t even understand what they’re are going through.

Serious question, is the MC retarded? He was abused by his maternal family since birth. The only person who ever cherished him aside from his servant was the ML, but still again and again he takes the side of his maternal family instead of trusting the ML. At this point I vote for the ML to take all his loyal and capable people and just leave, he'll 100% find a better partner that the MC