The wait is over! I couldn't decide on an ending, so I decided to write all of the ones that I couldn't decide on. You can pick the one you like best. Let me know which one it is! :)
Ending 1: Merthur
Arthur's breath was shaky as he leaned against Merlin. "There's something I want to... have wanted to say for a long time," he said weakly.
"You're not saying goodbye," Merlin told him, tears running down her cheeks.
"No, Merlin... Everything you've done. I know now. For me, for Camelot, for the kingdom you helped me build..."
"You'd have done it without me."
"Maybe. I want to say... something I should have said a long time ago. Since we first met. I love you."
"I love you too," Merlin smiled sadly. "I'll wait for you. I'll wait for you even if I have to wait for the rest of eternity."
"I want you to have this." With what little strength he had, Arthur held a ring out to her. The ring was beautiful. It was golden with the Pendragon seal in the center and diamonds engraved around it. "I know this isn't the best time, but... You're my other half, and I don't know what I would have died a million times if it weren't for you. Will you marry me?"
Merlin slid the ring onto her left ring finger. "Yes! A thousand times yes. I love you."
Arthur reached his hand up and rested it on Merlin's cheek. She bent down and kissed him on the lips. When they pulled away, Arthur smiled softly, and then his hand fell and he became limp in her arms.
"Arthur! No! Arthur! Stay with me! O drakon! E male so ftengometta tesd'hup'anankes!" She pressed her forehead against Arthur's and cried. "Arthur..."
(Time Skip- Lake)
Merlin watched as her best friend and love of her life floated away from her. "Arthur. In sibbe gerest." The boat caught on fire. Merlin fell to her knees and wept.
Merlin was surprised when Arthur proposed to her. He had never shown too much romantic affection for her. She supposed he did not need to. Their destinies were intertwined, after all.
Merlin did not return to Camelot. She could not bear the thought of being there without Arthur. Instead, she visited her mother for some time and then left to travel the world as she waited for her beloved. For her betrothed. He would return to her. Eventually.
Ending 2: Merleon
(This takes place after Arthur's death scene, which is the exact same as in the show)
Merlin walked numbly towards the castle. Leon and another knight were talking just outside. When Leon saw Merlin, he ran towards her and enveloped her in a strong embrace. Merlin buried her tear-streaked face in his chest as she hugged him just as tightly.
"He's dead," Merlin whispered. "They're all dead." Arthur was gone. Gwaine was gone. Mordred was gone. They lost... and yet, somehow, they won?
"I know."
The next month, Morgana, the last Pendragon, was crowned queen. It was somehow both solemn and joyous at the same time.
Merlin and Leon began spending more time together. They were the last of their group, after all. (Besides Percival... but I don't think anyone ships them.) Leon had always loved Merlin, and after a few months, she realized that she loved him too. Leon had always been there for Merlin when she needed him most, and he would continue to be there. A year later, Merlin and Leon married.
As the years passed, a shocking discovery was made. When Leon had been healed with the cup of life, he was gifted with immortality, as if the druids knew exactly who he would marry. Together, Merlin and Leon waited for the return of the Once and Future King.
Ending 3: Merwaine
(This takes place after Arthur's death scene, which is the exact same as in the show)
The first place Merlin went to after arriving back at Camelot was Gaius' chambers. After a tearful reunion with her mentor, she was led to the patient bed. Gwaine laid there unconscious, extremely beaten up.
"Is he..." Merlin was afraid to ask.
"He'll be alright," Gaius said. "It will take time, but he will live."
Gwaine did not wake up until just over a week later. The first thing he did was grin up at Merlin tiredly and say, "Princess." Merlin hardly ever left his side.
It was not long before the two wed. It was the happiest the kingdom had been since the death of King Arthur. Not even Queen Morgana's coronation could compete with the joyfulness of the kingdom on Merlin and Gwaine's wedding day.
(Percival had long since given up on his feelings for Merlin and Leon opted for the big brother role, knowing he could not compete with Gwaine.)
They lived happily for many years until Gwaine passed on. Once he was gone, Merlin left Camelot to wander the land, waiting not only for Arthur's return, but her husband's as well.
Wow. This book went on for a lot longer than I had expected. Thank you to everyone who stuck with me all this time. You guys are the best! Words cannot express how much I appreciate you. I love all your comments, they make my day! Yes, even the threats. Let me know what you thought of this book, good and bad, and if you have any requests, let me know! <3
(But seriously though. I don't have any ideas, so if you have any, please, please, please let me know. (I have a list of the fandoms that I'm in on my profile too if you want))
Also, a special thank you to @sherlockian_demigod , who is the one that gave me this idea. I just love her. Thanks Aukai!