Uther won Camelot when his avowed enemy bent a knee to him. Uther's heart swelled, knowing he had conquered every last piece of the kingdom -- from the newest babe to the oldest (and only) dragon. This was a kingdom made on rock and protected by steel.
Uther feels weak every time he looks at Arthur. Arthur is his Achilles Heel. Uther praises Arthur for his strength on the battlefield and castigates his son when Arthur shows tenderness towards individuals. It is the Kingdom and the People that matter, not a single person.
Uther used magic to beget his only son and that knowledge haunts him. He thought he could bend it to his will and paid a terrible price. His brief dalliance with sorcery scarred his heart. He thinks he commands magic, but he does not know that it will burn him again.
If Arthur is Uther's Achilles Heel, Morgana is his tender beating heart. He melts in her presence. All reason flees.
Morgana succumbs to no man.
Morgause owns her heart because they are sisters. She tends to the spark within her, nurturing it, not attempting to dampen it and make it die. Now Morgana understand that this is how you show love.
Kilgharrah was tricked and caged by a cruel jailer, but not broken. Freedom gained, he tries to dominate Camelot with flames, but Merlin calms his heart, soothes his rage. He submits only to the Dragonlord now.
Gwen has no need of metal armor like the knights of Camelot. She protects her heart until Lancelot wears a chink in it.
Gwen is both subject and ruler. She guides Arthur like a compass. He bows to her wisdom even as he holds her calloused hands.
Merlin loses a home when he leaves Ealdor, but gains one when he finds his destiny. He gladly relinquishes everything to serve Arthur.
If Arthur has learned one thing from Uther, it is to not show weakness. Arthur thinks it’s dangerous to place his heart in Merlin’s hands. He teases Merlin and derides him, because the deed is already done.
Like Uther, Arthur cares for his people above everything, but he is not Uther. Arthur has a tender heart; he sees individuals. This is his greatest strength. He has won his kingdom with love.