After knowing the Doctor for a while, Clara began to notice certain habits of his. He could never walk past a fez without putting it on. He has a soft spot for children. And he most commonly could be found reading a book anywhere on the TARDIS.
It wasn't until recently that Clara noticed that there were some books that he finished and others he simply abandoned part way through. She found it to be a curious thing and began to look through the seemed to be forgotten books. Clara was startled to find that they all had one thing in common: they all had strong romantic plots.
It prompted her one day as the Doctor messed with the TARDIS' console to ask a simple question. "Doctor, have you ever been in love?"
His expression immediately dropped and his eyes darkened. He went around the console and approached her. "What is wrong with you humans? All I want to do is share the universe with others. Show them the stars, and before I know it they are falling over me. I-"
"Doctor!" cut in Clara. "Don't go getting the wrong idea. I was just asking a simple question. I noticed that you never finish any books with major romances in them. I was just curious."
He took a step back and nodded. "Well then."
After a moment where no one spoke, Clara said, "Well…?"
"Of course I have," he said turning his back to her. He pretended to mess with a few switches on the console.
"What was her name?"
He closed his eyes for a moment and every memory of her flashed in his mind. He smiled a painful smile. "Rose, her name was Rose."
"Was she a time lord like you?"
"No. She was a beautiful human."
They were both silent for a moment. The Doctor continued to keep his back to her.
"What happened to Rose?" she asked quietly. Clara wanted to know, but she was worried of pushing him too far.
"I lost her," he managed to say.
"Doctor, I'm so sorry-"
"But then…" he began. He wasn't even sure why he was opening this old wound again, but the words kept flowing from his lips. "That smart, wonderful girl found her way back to me, and I had to do what was best for her. I was scared that I would have to watch her die. That I…I would be the cause of her death. So I let her go so that she would be safe. If I…if I could have spent the rest of my life with her by my side, I would have in a heartbeat."
Clara's stomach felt sick. She didn't realize how much pain the Doctor was in until now. It made her wonder how much more of that pain he kept hidden under those fezzes and bowties.
He finally turned around to face her now. His voice grew louder. "I should have loved her every day of her life. She deserved that. And you know what? I think I deserved that little bit of happiness too."
He turned away again and walked a few steps around the console. "River," he began, his voice was in a more hushed tone. "You met her."
Clara whispered, "yes."
"I cared about her. I could have loved her so much more. She deserved more from me. Maybe if I just let myself love Rose…then River…she would have found someone to love her like I should have. I should have loved that woman with both of my hearts. I tried, but…" He was shaking his head now. No more words would come.
"Oh, Doctor," Clara said walking over to him.
He stared at her for a moment and she gave him a big hug.
What he needed most was a shoulder to cry on. A part of Clara hoped that maybe he would feel a bit better now since he got some emotions out. The other part just wondered if it were the romances themselves or the happy ending that he couldn't bear.
She shuddered with that thought. It made her wonder why such a wonderful man, a man that does so much for everyone else, be denied a happy ending he truly deserves.