They had been so careful, sneaking around for months, making sure nobody knew they were seeing each other. If Gwaine showed up to morning practice with an extra spring in his step, the other knights just assumed he had had a very successful evening and night with a lady or two in the tavern. If Arthur, Gaius or Gwen noticed anything strange about Merlin's behaviour, he always managed to come up with some explanation or excuse. Keeping quite a few secrets for so many years had turned Merlin into a skilled liar if he needed to be.
It had all started after a drunken night at the tavern. Arthur and the other knights had already gone back to the castle, leaving a slightly drunken Merlin to deal with a fully drunken Gwaine. After he had finally talked him into leaving, Merlin had to support Gwaine all the way back. When they had made it into the main hall, Merlin had needed to make a decision: take Gwaine all the way to his room and then make his way to the other side of the castle to his own room, or trust Gwaine to find his room by himself and not fall asleep in a hallway again. Knowing the latter wasn't really an option, Merlin had dragged Gwaine behind him and had started to climb the stairs that would lead them to the Knights' quarters. When they had finally made it to Gwaine's room, Merlin had opened the door and had turned to Gwaine to push him inside. He had not been expecting the rather sloppy kiss Gwaine gave him, nor his own willingness to be kissed by Gwaine. Coming back to his senses, Merlin had broken off the kiss and pushed Gwaine through the door of his room. A muttered "goodnight" and Gwaine had shut the door behind him.
The next day had been awkward for Merlin, who had no idea if Gwaine even remembered the kiss. He had tried to avoid Gwaine, who had not been happy being avoided by his friend. A rather heated argument in a deserted hallway had brought out the truth: Gwaine had not been as drunk as he had made everyone believe, and he remembered the kiss with Merlin perfectly. The knight had been attracted to his friend for a while and had thought of no better way to find out how Merlin felt about him.
"When you broke off the kiss and then started avoiding me," he had said, "I figured you weren't interested."
"You dollop head," Merlin had said, pushing Gwaine against a nearby wall and pressing his lips against the other man's mouth.
They didn't have one specific location they used for their secret meetings. They tried to split their time between Merlin's room in Gaius's quarters and Gwaine's room in the Knights' quarters, but in the past few months, they had found many quiet corners in the castle. Like now, when Merlin had just left Arthur's rooms after serving him dinner, and turned a corner, only to have Gwaine pull him into a small alcove.
Before Merlin could say anything, the knight dropped down on his knees, taking Merlin's trousers with him. Holding on to Merlin's hips, Gwaine took Merlin's cock in his mouth. Knowing he couldn't make any sound, lest the guards came over to investigate, Merlin had to resort to biting down on the knuckles of his left hand while he ran his right hand through Gwaine's hair and clutched it tightly in his fist. Gwaine kept bobbing his head up and down, occasionally letting Merlin's cock escape his mouth entirely so he could kiss and lick and tease his way down his cock, exposing it to the slight draft that was always present in the castle hallways. The contrast between the cold air and Gwaine's hot mouth (and wicked tongue) brought Merlin closer to the edge. When Gwaine went back to bobbing his head up and down Merlin's cock, he felt a second hand running through his hair. He knew Merlin was close when he heard a whispered moan of his name and some garbled sounds. Gwaine kept sucking, and when Merlin came, he swallowed around Merlin's cock, careful not to spill a single drop. Merlin clutched Gwaine's hair a little bit tighter before letting go of it completely. Gwaine brought one of his hands to Merlin's cock, to help milk the last bits of seed from him, the other hand still clutching Merlin's hip. Satisfied with his work, Gwaine let Merlin's cock go and looked up. Merlin had his eyes closed and was using the wall behind him to keep his body upright. Gwaine couldn't supress a smug grin and a chuckle as he got up, helping Merlin fasten his trousers again.
The grin and chuckle made way for a low moan, as Merlin had regained enough clarity for him to run the back of his hand down the front of Gwaine's trousers, firmly pressing against the obvious bulge there. As Merlin's right hand made its way inside his trousers, Gwaine let his head fall against Merlin's shoulder, breathing heavily against his neck. Merlin started stroking his cock, tantalisingly slow at first, but picking up speed when he felt Gwaine move his neckerchief out of the way so he could mark his neck. Merlin's other hand grabbed a hold of Gwaine's behind, dragging his trousers down just enough for him to have easier access to his entrance. He ran his fingers down, down, down, pressing one digit against the puckered hole. Gwaine had started to bite down on Merlin's shoulder in an effort to keep quiet, as Merlin stroked his cock faster and faster, slightly twisting on the upstroke. He pushed one finger inside of Gwaine, feeling and hearing his breathing get heavier. He added another finger and moved them in and out at the same pace as he was stroking his cock, bringing Gwaine closer and closer to the edge. Merlin moved his head so his mouth was against Gwaine's ear.
"Come for me," he whispered, grasping Gwaine's cock even tighter.
Merlin's voice, his smell, his hands, his fingers, it all became too much for Gwaine. He bit down on Merlin's shoulder and felt himself spill inside his trousers. He tensed around Merlin's fingers as Merlin kept stroking him through his orgasm. Completely spent and leaning even more against him for support, Gwaine felt Merlin slide his fingers out of him. Merlin removed both his hands from Gwaine's trousers and, making sure he had his full attention, brought his right hand to his mouth. Seeing Merlin lick the come off of his fingers made Gwaine groan. He lifted his head and captured Merlin's lips, tasting himself on them. He was panting when he released Merlin so he could rearrange his trousers properly again.
"Meet up again later tonight?" he asked, fiddling with Merlin's neckerchief so it would cover the marks he left on his neck.
"I need to help Arthur with something first," Merlin said, "but come find me in the library. Geoffrey will be gone by then."
Gwaine grasped Merlin's head between his hands and kissed him briefly before whispering a quiet "see you tonight" and leaving the alcove.
Merlin waited a few minutes, collecting his thoughts – 'What was I supposed to be… Right, helping Arthur.' – and then leaving in the direction of the kitchen. He was going to need all the energy he could get for what he was planning to do to Gwaine later.