Just a little idea that I had. Enjoy!
Over the past few years Arthur learnt that whenever Gaius said Merlin was in the tavern it wasn't some kind of excuse for his menservants sudden absence, but meant that Merlin was deeply troubled by something and needed his help. Arthur had first discovered this when after the Bastet had attacked and been killed.
"Gaius!" Shouted Arthur as he burst into the Physicians chambers.
"Where is Merlin?" He asked irritably. He then laid eyes on the Old man. He looked weary and more worried than he had ever seen him before.
"Merlin's alright. Isn't he?" He spoke again. Jumping to conclusions, just as he always was.
"Hopefully." Gaius responded. "He's in the Tavern, sire" And he returned to whatever he was doing before.
Any concern he held for his frien- manservant instantly dissolved and anger quickly filled the space. He was so absorbed in his own thoughts he completely missed Gaius calling to him as he left.
"Bring him home Arthur. He needs help"
Arthur stormed down to the Tavern and burst in. It was empty apart from a few people who had passed out the night before. One of the face very familiar, Gwaine. He shoved the drunken, and slightly hung-over, knight roughly to wake him up.
"Gwaine. Have you seen Merlin?" He asked, still agitated at Merlin's little escapade. Gwaine shot up straight away at the mention of Merlin's name and looked directly into Arthur eyes.
"He's in the corner. Look after him will you?" Gwaine said, concern lacing his voice, whilst pointing to a figure hunched over a tankard in the corner. Arthur was confused by what Gwaine said so he brushed it off. Arthur stomped over to the corner where Merlin was sat but was stopped short when he heard sniffling and that Merlin's shoulders were bobbing up and down. Was he crying? Arthur thought. He slowed down and knelt beside his distraught friend. Merlin didn't even seem to acknowledge his presence. Arthur preceded to pry the tankard out of Merlin's hands and helped him to his feet and out of the Tavern. According to the owner he had been there since Arthur had dismissed him the previous night and all he had down was drown his sorrows in tankard after tankard.
At some point during the way back his, still very drunk, friend had fallen over and Arthur had to resort to carrying him back, bridal style. On the way back Merlin kept murmuring something about a girl named Freya and how she was dead. Arthur guessed that she had been killed during an attack recently, most likely killed by the Bastet.
Arthur brought him back to his chambers and laid him in his cot. He then told Gaius what had happened and told him to tell Merlin that he could have the rest of the day off.
That was only the first time that Arthur had to collect Merlin after he had spent the night drinking to forget his heartache. It happened often and Arthur wished that Merlin would confide in him. Some of the nights were worse than others, for example the night after Morgana was taken away by Morgause, Merlin went missing for days and came back very, very drunk. It was the same after the attack of the Dragon. As Arthurs reign progressed further and further Merlin's visits to the tavern became more and more frequent. All Arthur could do though was to be there to bring him home every time and that is exactly what Arthur did.
Before all of this happened he used to think that Gaius' excuse 'he's in the tavern' was exactly that, an excuse. That was before he saw how much his friend held on his shoulders. And now Arthur saw how much he truly cared for Merlin and that he would always be there to carry him home.