Imagine Arthur hates Merlin.
No no, wait, it's not about magic this time and it doesn't contradict his love for him, just -
He hates that Merlin is always right.
He hates that Merlin is the only person he can trust, is the only person always honest with him, who always puts him first.
He hates that Merlin is unavailable. Too far away. Born too lowly, born a man.
And he hates that Merlin is always the one who brings the bad news. That Merlin tells him who betrayed the crown. That it's Merlin who spots evil before Arthur is ready to even consider it. As I said, Arthur hates that Merlin is always right.
And maybe he begins to connect the bad stuff with him. To associate Merlin's truth with disaster. It hurts to see him. Carefree, clumsy, wonderful Merlin, who knows Arthur's biggest flaws, who told Arthur and forgave him for not believing him, for causing deaths.
So, when Merlin's magic is revealed, a part of Arthur is relieved. That not all of it was always the truth. That Merlin made mistakes too that are just as consequential as Arthur's own. A part of Arthur is glad that the worst, most hurtful betrayal reveals only that Arthur's shame had never been only his to bear. That finally, he has someone to share it with.