In medieval times, in Merlin, Arthur and the other knights slap each other, sit super close, and whatnot. Probably would slap each other's arses, if they weren't always wearing chainmail.

So, Arthur slaps the knights on the edge of their shoulders. But with Merlin, it's always close to the neck/shoulder joint. Can't quite keep from cupping Merlin's face and confessing his love.

Well, I think.

Obviously all their touches are deliciously unnecessary.

And Arthur always looks inexplicably (pretty explainable, actually) sad when he says stuff like, "we can't be friends," and that one scene when he thinks Merlin has feelings for Morgana, and he says, "she can't be your friend, let alone anything else," but it was contemplative and sad like he wasn't really talking about Morgana...