He had just killed his father, the least he could do was wait for him. Merlin knew exactly how Arthur felt. When he had lost his father he felt grief stricken and lost, even though he had never in his life known him. He hadn't known his father for that long, and already he had idolised him, he was somebody he could look up to and admire in a matter of hours. Arthur had looked up to his father for his entire life and Merlin had killed him. As much as Gaius told him that even without Merlin's magic Uther would have died for his injuries anyway, Merlin could not help but feel like he was wholly responsible. If Merlin hadn't jumped for the chance to perhaps change Arthur's views on magic being outlawed, Uther would have passed away peacefully and Arthur's view on magic would have been no different. But instead, Merlin felt more alone than he had previously now Arthur felt so strongly against magic. He should have just let it lie. But in hindsight, Merlin would do anything to help Arthur and if healing his father with magic meant helping him, he would do it in a heartbeat, every single time.
Merlin thought that after successfully healing Arthur's father, he would tell him that he himself possessed magic. That he had saved Arthur's life countless times. That without magic, Arthur would surely be dead. Before he had tried to heal Uther he was so certain that his plan would work, and Camelot would welcome magic with open arms. People wouldn't be scared of the magic the possessed anymore and would come out of hiding, no longer fearing for their lives. But Merlin, stupid, stupid Merlin, had made the already dire situation much worse. Witches and warlocks would have to stay in hiding more than ever because of Merlin's stupid mistake. He would have to hide his powers with more skill, for fear if he was caught that Arthur, who he considered as a friend, would have him executed. As much as he admired Arthur for his courage, he believed that if he found out that Merlin was a warlock, he wouldn't hesitate to have him killed. Thinking about that was making Merlin's mood worse, but he could not for the life of him keep those thoughts from running around over and over in his head.
But no matter how much Merlin thought about it, Arthur was his friend in the here and now, and as long as he didn't find out Merlin's magic it would stay that way. And right now Merlin had to help Arthur get over his grief. In the morning he'd tell him how sorry he was about the whole situation, that if he could he would turn back time to bring Uther back, no matter how harsh he had been on Merlin in the past. Merlin blinked hard, the onslaught of sleep coming to the fore, but instead of going to bed he was going to stay put. For Arthur. For support.
After all, he had just killed his father, the least he could do was wait for him.