Yes, Merlin had saved his life. Merlin had probably saved his life back in Camelot, as well, more than once. How humiliating!
Magic wasn't illegal in England. Arthur wasn't sure what to do.. There wasn't really anything he could do. There was no one to report it to, which was almost a relief. He wouldn't have wanted to turn Merlin in to be executed. For all of Merlin's failures he was...well...Merlin.
Still, it didn't sit right with him. "You lied to me," Arthur said, frowning. For a moment he looked more hurt than angry. "For years!" He'd trusted Merlin. There were things he told Merlin that he didn't tell his own father.