Arthur and Merlin are hunting in the forest or at a banquet. *insert banter here.*
Bandits/evil sorcerers/magical creatures attack and threaten Arthur's life! Arthur, despite being a practiced swordsman and skilled hunter, is unable to defend himself for some reason!
Merlin selflessly uses magic to save Arthur, at the cost of revealing himself.
Arthur cries "BETRAYAL!" and imprisons/exiles/executes Merlin.
Arthur becomes moody and remorseful after talking to the Knights/Gwen/Gaius and learning about all the things Merlin did to defend Camelot.
Arthur, being the BEST KING IN THE HISTORY OF ALBION, comes to the conclusion to generously and selflessly forgive Merlin's "betrayal".
Merlin is released from the dungeons/returns from exile/comes back from the dead and is reunited with Arthur.
Instead of apologizing for any actions, Arthur demeans Merlin as a sign of "affection". This is not an abusive relationship. Nope, not at all.
*insert gratuitous sex scene if slash (which, let's be honest, it probably is)*
Around the same time, by sheer coincidence, Camelot suddenly goes to war against Morgana/neighboring kingdom and needs Merlin's help to prevail.
Merlin unleashes his power to fight for Camelot, because nothing says "acceptance" like using magic as a deadly weapon!
Magic is legalized again, yay? There is no fallout from this whatsoever.