Merlin is actually really proud of Arthur. You can't lie it is impressive. Love how Merlin is so smitten with Arthur he can't hide it AND if only somebody asked "what is even that special about him"... oh they wouldn't hear the end of it. Arthur's every victory feels like his own, all the decisions the good and the bad. You just don't merge with one's life like that if they are just a friend.
And this scene perfecrly shows that Merlin's opinion matters to Arthur. On everything. Even something as small as yet again winning during practise. And Merlin could compliment him every single day and the next day Arthur would ask again. He needs reassurance all the time, the emotional support from that one special person. He needs Merlin to tell him he is doing the right thing, that he is good and competent. I am forever with you two lovesick boys.
