Disclaimer: I do not own Merlin. If I did, it would probably be called Morgana. :)

Author's Note: Spoilers through season 3 (especially "Queen of Hearts" and "The Coming of Arthur Part 1"). This is going to be a three-shot with each part based on something Morgana knows about her friendship with Guen in season 3: 1) that Guen is her weakness, 2) that Guen will side with Arthur, and 3) that Guen will be her downfall. I try to stick to the show as much as possible, but some of it will be a little AU just because I don't think that Morgana could be friends with Guen that long and then suddenly not care for her anymore, even after being with Morgause for a year. Let me know what you guys think. Enjoy!

Weakness

Morgana had always known that Guen was her weakness.

There had never been anything she would not do for her friend. It was for Guen that she had stood up to Uther and spent the night in the dungeon. It was in revenge for the death of Guen's father that she had first agreed to help kill the king. It was for Guen that she had let the knights drag her away from the druid camp and back to the prison that was Camelot. It was for Guen's sake that she kept her defiance as simple and as secret as possible. It was for Guen that she had fled their captors alone, and it was for Guen that she had begged Arthur to defy his father and find them again. It was for Guen that she had stayed in Camelot when she could have run. Because Guen was the one person in the whole world who she really truly cared about.

There had once been a time she had felt a strong kinship with Merlin. There was just something about him that was so easy to trust, to confide in. He had worked his way into her heart. But when he stabbed her in the back, she had forced herself to let him go. He had chosen his side.

Gaius was much the same. She liked the physician, she really did. He had been good to her over the years, far better than she deserved. But she knew from experience that he would stand by Merlin. He too would not hesitate to cut her down in the defense of his king. And that meant he would have to be dealt with.

Arthur had taken a bit longer to get over. As much as they fussed and argued, she really did love him deep down. He was the brother she never had. And in all honesty, they really were quite close, despite the way they acted. But she knew in her heart that he would stand by Uther. He always had. True, he had helped her smuggle Mordred out of the city. And it was true that he had gotten her out of the dungeon. And it was also true that he had defied his father to rescue Guen, among other things. But how many other executions had he watched in silence? How many others had he allowed to die? He would stand by Uther to the end, and that made him the enemy. It had taken her a few months to get used to the idea, but she had finally accepted it. If it came down to it, she knew she could kill him without hesitation. But she also knew it would probably haunt the corners of her mind for years to come.

Guen, however, had been another story. No matter how she tried, she simply could not accept the possibility of having to destroy Guen. Guen, her best friend, who had been kinder to her than anyone alive, who kept all of her secrets and had covered for her more times than she could count. Guen, who went out of her way to make her smile, who had pulled her from the nightmares and done her best to calm the raging fears, who had held her as she cried and joined her when she laughed. Guen, who had always been there, no matter what, and who had always trusted her. She simply could not bring herself to accept the idea of hurting her friend.

When she finally returned to Camelot, she had worn a carefully constructed mask. She had pretended to forgive Merlin and pretended to be overjoyed to see Uther. She had reminded herself not to let Arthur get to close or to buy too much into Gaius' kindness. But with Guen there had been no acting. She had wrapped her arms around her friend and held on tight as joyous tears ran down Guen's face, truly glad to be back in her friend's arms.

And then she had begun to walk the tightrope, trying to balance her friendship with what she knew had to be done. She had forced herself to lie to Guen despite the way it tore at her heart. She had been cruel and cold and distant on occasion, trying to keep Guen from getting farther into her heart. It never worked. She had watched Guen getting closer and closer to Arthur, knowing that someday she would have to break her friend's heart. And that thought nearly broke her own.

She had played along with Morgause, allowing Guen to be kidnapped and forced into the position of choosing between Arthur and Elyan. Then she had seen the marks on Guen's wrists, and she had felt her anger rising. The pain in Guen's eyes as she tried to choose had almost been too much to bear. Had she really done this to her? Somehow they had all come out of that one alive, and, despite the fact that Merlin had ruined it all, Morgana found that a small part of her was glad, if only because Guen was still smiling.

Then she had dreamed of Guen being crowned, and Morgause had urged her to break them up. She had expected her plan to get Guen banished. That came as no surprise. But when Arthur decided to go with her, Morgana had panicked. She had devised the poultice then, hoping to deter him. That had gotten Guen sentenced to execution. At first Morgana had thought she could live with it, but the thought of a life in Camelot without Guen had finally become too much. She had confronted Uther in private, insisting that Guen could not possibly be a sorcerer and begging him to spare her, but to no avail. Guen was doomed. And then the strange sorcerer had appeared to take responsibility for her actions, and Morgana had nearly wept with relief. But the damage, it seemed, had already been done. Guen pulled away from her and the warmth in her eyes dimmed, as though she suspected something. That was when the true realization had crashed down on Morgana. It would be impossible to hold on to Guen and still stand by Morgause and save Camelot from Uther. She was going to have to choose between them.

She awoke that night in tears, knowing what she would have to choose. Guen had been there like always, and after some hesitation she sat down beside Morgana and held her, trying to soothe her. Even after everything she suspected Morgana of doing, Guen still could not bear the sight of her crying. The feeling of her friend's arms around her just made Morgana cry harder. She knew that the day was soon coming when she would have to commit the act that Guen would find unforgivable, the act that would drive them apart forever. Part of her wished that day would never come. But even she could not stop time.

She had tried to distance herself after that. She had played the part of the old Morgana while secretly building walls against Guen. And then the time had finally come, the time when they would take Camelot and make Uther pay for his sins. Morgana had found Guen by the window just before the army attacked. Something in that moment had compelled her to reach out, to give her a chance, to ask her to join them. And so she had offered Guen the promise of safety if she stood beside her. And by some strange twist of fate, Guen had accepted.

Morgana knew in her heart that it could not last. She knew that if the moment came, Guen would turn on her. She knew her friend would never be able to forgive her for what she was about to do. But she was so desperate to hold to their friendship, so desperate for Guen to stand beside her, that she closed her eyes and let herself believe for just one moment that it was possible, that Guen would not stab her in the back like Merlin, that they could stand together as they always had. Even though she knew in her heart that it could never be.

Morgana had always known that Guen was her weakness. She knew she could afford to have none, that she had to let her go. But she could never quite bring herself to do it.

Let me know what you think. If I get some decent feedback, I'll post the next part. :)

Also: Not really sure how I feel about the main title... If someone has another idea, let me know!