This is horrible, honestly. Necessary, but horrible. Merlin, trying to pretend it's all normal, like it was before Arthur started dying, like it was before Arthur found out about him. Joking with Arthur just like he used to. And Arthur, trying to ignore that for the past five years of his life his best friend has been hiding the truth, has been covering who he really is from him. It's one of the very most heartbreaking scenes of the whole show.