Merlin's POV
He knew that Arthur cared about her and ultimately was more compassionate than his father ever was or ever would be. He had expected him to go after Gwen even against Uther's express wishes because that's what real friends did for each other. What he didn't expect was Arthur's earnest declaration of feeling for Gwen which came out of his good-natured teasing.
So now that he knew the truth of Arthur's emotions, he could sense the change in energy, the heightened importance of finding Gwen alive and well to return her home.
He knew the Arthur of old would have given little thought to the well-being of servants and if he was being honest, Gwen would never have registered on Arthur's consciousness had she not introduced herself whilst he had been held in the stocks and subsequently becoming friends with him.
It said a lot that Arthur had willingly risked going through those forsaken Tunnels of Andor to hasten their rescue attempt. He had been more than a little upset when his master had revealed his surprise that the gaia berries had worked on misleading the wilderen but that surprise had been nothing compared to finding Lancelot with Gwen!
Racing through the escape tunnels of the Mercian castle, there hadn't been time for explanations but as Arthur broke the chains and forced open the grate, he had turned round in time to see that one gesture. It was so simple and so brief but filled with an intimacy that could only be guessed at. He remembered meeting Arthur's eyes after he too had seen the same sight and his heart tugged in sympathy at the stunned look in that blue gaze which had lost its usual confidence.
Around the campfire, he saw the old swagger and cockiness return to Arthur but somehow, it was less convincing this time as he answered Lancelot's queries. He saw Gwen's poorly-disguised hurt at his final remark, saw the immediate shame that overcame Arthur and he saw the comprehension that appeared on Lancelot's face. He saw more than most people gave him credit for and he could not lie when Lancelot had asked him the true nature of Arthur's feelings for Gwen. It hurt to hear the knight say he had to leave her. He liked him and thought that the kingdom would do well to have more men like him around but he also understood his reasons for going and it was not his place to prevent his departure.
Telling Gwen in the morning had been heartbreaking. Seeing her cheerful, hopeful expression crumble into abject loss was almost too much to bear and he felt wrong repeating those poignant words to her. Those words should have been coming from the lips of another.
When he heard Arthur call them to restart their journey, he wanted to shake some sense into him, prince or no prince. What Gwen needed was to be reassured that her love was being reciprocated, that she had never been abandoned, especially not by him. What she did not need was a brusque order to get going on the road again and a tensely silent ride home.
In a way, he was almost glad that he had been left to walk. The pain in his feet distracted his mind from dwelling on the tangled situation of his two friends.