Rose watched as the Doctor raced around the counsel, and she was always worrying about him. She watched him run around and click the buttons and go on and on about why certain planets were the best for chips, and why certain planets were the worst. He had his trademark "Im the most impressive time lord you know Rose" look on his face as he did his dance.
900 years, over 900 years he had been doing this. Running around, saving lives, being impressive, traveling with people. After meeting Sarah Jane, Rose had done some snooping. The Doctor had traveled with many before Rose, they always ended up being close friends, he always lost them.
When Rose looked into the heart of the Tardis it changed a lot about her that Rose was afraid to mention to the Doctor. She saw how he looked at her when she promised him forever. She had a time limit with him. He was counting down the minutes till he lost her, her time Lord always ending up alone in the end. With what had happened Rose knew her promise for forever would be able to be kept. She knew she could be with him for as long as he needed her.
She would fight tooth and claw to get back to him. If she ever lost him, Rose would get back to him.
"Rose-"
Rose looked up, wide eyes. The Doctor had a concerned look on his face.
"Rose are you alright?"
Rose smiled and shook her head.
"Of course I am Doctor." She beamed at him. "Now what were you saying about getting me some chips?"
He beamed back and went back to driving the Tardis in a whirl of blue and red.
Rose knew for certain then.
She would be with him forever, no matter how long she had to chase him to make forever happen.