He felt it the moment he woke up after regenerating. This body was different from the rest. No. Not the body. Sure this body was older than anything he had been used to in hundreds of years. But the body wasn't the issue.
It was the mind.
This mind, these new thoughts. They were different. Darker. So much darker.
At first he thought it was because he had just regenerated. His mind wasn't quite straight. And after settling down into this new him, all those dark thoughts did seem to go away. And everything went as usual. Just him, Clara, and his beautiful Tardis off to see the universe.
Clara stayed with him, of course. She had promised him before he had regenerated that she would stay with him to help and protect him, and he was going to hold her on that promise. Not that she complained.
Their relationship had changed. That wasn't a surprise. Gone was the flirting to be replaced with a familial relationship. She would tease him about his new fatherly tendencies. He would scold her for teasing him and in return she would tease him some more. At times it annoyed him. But mostly he was just happy that she was still comfortable around him, that the basis of their relationship hadn't changed.
Things weren't always this easy, though. There would be moments, during their adventures, where he would do something that she didn't approve of. She would say that the old him wouldn't do things like that. And it angered him. Because he wasn't that bowtie wearing, arm flailing kid anymore. He was older now, gray hair, worn skin, a presence that intimidated everyone.
It was times like these where he doubted her affection for this new him. She didn't stay because she cared about him. She only stayed because she had made a promise to that other him. That damn promise. But he never confronted her for it. Instead he'd distance himself from her and they wouldn't talk for hours. After a while they would bump into each other and everything got better. She was always the first one to apologize.
Soon things started to go wrong. They would get caught in too many dangerous situations. He would make decisions. And people died. Sure people always died wherever he went. But this time it was different. Because this time… he didn't care. People died and he couldn't bring himself to care like he used to.
Their fights grew more frequent and more violent. It used to be all about glares, pouts, and stern whispers. All that turned into shouts and slamming doors. But he never struck her. No. That was one thing he would never do.
Instead he alienated her. He wouldn't show up for weeks and when he did, it was only for one small adventure. Just a courtesy. She would ask him why he didn't come as often. To which he would lie and say that the Tardis didn't take him to the right times. She obviously didn't believe him, but she never pushed.
They went on like this for many months. But he grew frustrated because he couldn't understand. Every time he came back she acted as if nothing had gone amiss. She was always just as excited, just as willing to join him like before. But why? He knew she was only coming along because of the promise. And it confused him that she still seemed to enjoy it. And it angered him to think that she was putting an act. Why was she doing this? Why would she still come with him?
"Because I promised." She startled him. He didn't know she had been so near.
"But you didn't promise me."
"No, I didn't. I promised him." She smiled tenderly and cupped his face with her hand and for the first time in a long while, he actually came to believe that she really did care.
"But I kept it for you."
Author's Note: I've been awake for the past 22 hours or so studying for two tests that I just finished. Needed to write this cuz it kept nagging my mind the whole time. Sorry if it doesn't make sense. I'm tired. I'm going to sleep now. Bye.