Merthur being idiots in love aka self sacrificial
Being attacked and left in the middle of a forest to die is not how Merlin imagined his birthday would be spent. However, when he sees Arthur being in that critical condition, there's not much else to consider but to fix the problem. How can he ensure Arthur is safe? He is breathing so faintly, barely concious with so much blood loss.
Merlin isn't doing much better himself but that's not the point. He knows he doesn't have enough strength to use magic at this stage. But if he used up all his energy, his magic and life force, there's a chance he can save Arthur. He'll take his chances, thank you very much. As for hiding his magic, he couldn't care less at this point. Yes Arthur will be angry, almost feral when he realises and recognises Merlin for the monster he is. But he certainly would rather spend all his energy to transport Arthur to Camelot. After that, it's not like he'll survive anyway. Maybe that betrayal would help Arthur in his grief. (yes, he'll see that Merlin's loss is not worth spending much time over). He knows what he has to do now. He looks at Arthur one last time. Sees him a bit wide eyed and exhausted, trying to roll towards him. He smiles at him one last time. It always has been for you, Arthur, he thinks. My magic, my loyalty, me. It was my absolute honor, serving you, Sire.
Arthur is trying really hard to hold on to his consciousness. He really is, especially after Merlin smiled at him. That idiot! He knows that face. It's his 'I will do whatever it takes because it is the right thing to do face'. He sees his stubborn set of jaw, his shoulders rolled back, as his eyes turn golden..What?! Everything seems to click in slow motion for him. Merlin, despite bleeding and injured as bad as he is, looks positively radiant. He has magic! Right now, covered in blood, oozing out golden light from his body, it seems more apt to say he is magic, rather than he has it. However, he hasn't much time to think of it. Merlin's focus and his determination alarms him. There's definitely something insanely stupidly self sacrificial about it. He can feel his panic rise. In his fear, he instinctually rolls over with all his energy as does the one thing he can think of : hold onto Merlin. Whatever is happening, he knows in his heart he can face it if Merlin is with him, by his side, where he always wishes him to be.
He sends for Merlin. He needs to make sure how to keep him safe. He can't think of what would happen if news of Merlin's magic gets out. He arranges the funds to send him away, speaks to someone he knows so he can work. He also makes it that it's halfway between Camelot and his hometown.
Merlin enters. Worn out, dark circles and pale skin. It pains him physically to see him this way. At least he has a trusted horse to take him where he needs to be, with enough money that he can sustain himself comfortably even if he doesn't work at all the coming couple of years.
Merlin's shoulders have a resigned droop, his eyes a sign of quiet peaceful resignation. Arthur wants Merlin to sit comfortably, have a healthy plate and then discuss his plans. Alas he can't afford such a luxury when every minute is an added risk. He had waited for Merlin to recover just enough and it was already 3 days too many.
Merlin walks slowly but surely. However what he does next makes Arthur startle a step back. Merlin comes close enough to him, makes very very brief eye contact, enough to give him a small smile and then kneels! He has his hands behind his back and head bowed enough to almost touch Arthur's ankles.
"Sire, I accept the consequences of what I am. It was my absolute honor to serve you. If you will let me can I ask of you one last wish before I meet my end?"
Arthur has no idea how to respond. What is Merlin talking about? What end ? Sure it might be his last time in Camelot, but Arthur knows and can feel Merlin means something more than that. He's trying very hard not to acknowledge what Merlin is thinking. Merlin takes his shock as hesitation. His face twists before it clears with renewed perseverance. "Please Sire. Gaius has nothing to do with what I am. He's old enough to be spared seeing me burn. If you'll only grant my request to make this a private affair, I'll be infinitely grateful for it"
With horror, Arthur moves with the intention of pulling Merlin up. But he only bows further to touch his forehead to Arthur's feet.
Arthur CANNOT take this anymore. Merlin really thought this of him? after all this time? and came to him like an animal to be slaughtered? His blood boils. He always knew anger is his worst enemy.