Guilt
"This was not meant to happen."
Something went wrong, so terribly wrong. The spell the warlock had used, was designed to heal. Someone had messed this up. Something had happened. Merlin kept running. He needed to run, Arthur would catch him and kill him. This was his fault. A tear escaped his eye. It splashed on the white corridor floor. Then he stopped. He had reached the King's room. He wiped his tears away, and dried his eyes. He couldn't be seen crying.
The door swung open, slamming quietly off the wall. No one looked up. Everyone grieved around the King's side. Merlin caused this mourning. He had gone and messed up the whole future. Why didn't he listen to Gaius? It seemed so right at the time! Arthur eventually looked up, his face shining in the candle light. All emotion was displayed across his face and Merlin was sure he heard his heart break.
"The King is dead." Gaius informed Merlin. Merlin bowed his head, his tears did not flow.
Now, the warlock would have to hide for the rest of his life. He was to blame for all of this. Every druid, every human and creature looked up to him as Emrys, waiting for their turn to shine, for Albion to free. That time would never come.
Merlin would never forget this.