#3: Arthur
Disclaimer: [Insert standard disclaimer here]
Summary: Arthur had trusted Gwaine...but then, he'd trusted a lot of people.
He'd been betrayed too many times.
He'd been betrayed, over and over again by people he thought he could trust. His friends. His allies. His sister. His uncle.
Even by his father.
When Morgana had claimed the throne, proclaiming her enmity to old Camelot, Arthur had felt that everything had come to an end. There was nothing left.
Somehow, the strangely wise words of his manservant had snapped him out of it. But the sting of betrayal remained.
So when one of his most trusted knights admitted to being close to magic, a force he despised, something inside him snapped.
So he banished Gwaine and decided never to speak of him again. That worked so well...