He watched Arthur start to leave, and for an instant he did look a little ashamed of the fact that it might have taken him years to tell him the truth. Not that it lasted longer then an instant because Merlin definitely had something to say to that.
"You spoke to me as well. I was still your friend and adviser many years after that." He faintly recalled memories from his older self -- a long time of silence between them after he'd told Arthur in Camelot as well. He hoped that didn't happen here.
"I've risked my life for yours several times, and you've done the same for me. I even used magic to heal your father knowing that if he woke up, I'd be found out. I confessed, you laughed and called me an idiot. I used it right in front of you, but Will took the blame to protect my secret, and you were upset with keeping it from you because magic was dangerous." He was rambling again and at some point had moved between Arthur and his way out of the room.
"All that and you can't forgive me for this one secret? I can tell you the truth about everything since we've met if it would make you feel better. Like when I drank that goblet of poison, and despite slowly dying I sent that light to guide you out of the cavern. Or I could show you the scar from fighting the sorceress that still hasn't totally healed. I'm your friend, I am happy to be your servant, and I want to see you become a great king. So --" Was he finally lost for words? There was something he was trying to say, but it was like it got lost in the madness of his panicked speech.
"So stop being such a - a prat!" He finally took a breath and stilled. Looking a little bit desperately at Arthur to change his mind.