I wrote this ages ago for somebody on tumblr long before the episode where he hugs the tree (It was the very first piece of Artree fanfiction). Artee. I shipped it before it was cool.
Arthur ran his fingers against the long arm of his beloved. She felt smooth to his touch with some hints of rough edges. Arthur didn't mind. This was what made her, her. As he stepped closer to her he wrapped his arm around her delicate waist. She fitted in his arms perfectly. It wasn't often that Arthur came to the forest alone but when he did he got his beloved and was always mesmerised by her beauty.
Leaning his head against her delicate figure he took in her scent. Trying to imprint it to memory. She smelt of nature. The beautiful fresh pine smell that he had become accustom to upon these visits to her. It would linger on his clothes for awhile. Even when he did return to Camelot. His court would think he was weird when he would causally lift his cloak to him and take in a deep breath. He didn't care though. It made him think of his beloved and he felt contempt.
Arthur softly planted kisses upon her skin. Trying not to neglect any part of her. This was for her, all for her. Arthur's turn to pleasure her. He didn't care as long as he just got to hold her. After all the worry and all the danger in Camelot the thing that seemed to calm him was escaping to visit her. She may have been forbidden but he couldn't stop. He loved her too much.
When time came for Arthur to leave he gently kissed his beloved and whispered his quick return to her. As he walked back Camelot he looked over his shoulder, trying not to loose her from his sight. She never moved. She never left. That's what Arthur liked about her. He could always count on her to be true to him, to never leave. This fact reassured him as he finally tore his glance away and left his beloved to the mercy of the forest.
Merlin finally emerged from his usual hiding spot within the bushes. His glance following Arthur's trail back to the castle. He often followed Arthur out here on his visits to make sure everything was safe. At first he had been terrified of his discovery of Arthur's activities but had soon grown accustom to it. Arthur was happy and even though many of his subjects would not understand it, Merlin did. It worried him sometimes and even upset him slightly. He would love for Arthur to treat him so. For him to be Arthur's beloved. Instead he was the loyal servant trying to please his master. It didn't bother him that much. As long as Arthur was happy with his beloved. Even if she was just a tree.