I was watching the impossible astronaut last night and saw at the end it said in loving memory of Elisabeth Sladen. I started crying. So this morning I though of doing this. I was crying while writing this.
By the way, if you don't know who Elisabeth Sladen is, it's the girl who played Sarah-Jane Smith.
When I was writing this, I was listening to music, and Forver Young by: Jay-Z and mr. Hutson came on so I started to cry. It was sad!

It was a normal day in the TARDIS. At least, it was until the phone rang. The Doctor ran over to the phone and answered it.
"hello?"
"yes this is the doctor."
"oh." He hung up.
Sarah-Jane had died. She had died of cancer.
"Doctor, what happened?" Amelia Pond said.
"Yeah, you just kinda got all sad," Rory said.
"One of my old companions died. She uh, ment a lot to me."
Why does this always happen to him? All of his companions always leave. Even of they don't want to, they still do. But with Sarah, it was different. He left her. She came back.
He could never see his beloved Rose, or best friend Donna again. And now, Sarah.
He could always see Donna from afar or Rose may some way find a way back-even though it's impossible- but Sarah-Jane, she...she died. Gone forever. Goodbye.
The last time he saw Sarah was the last time he saw Rose too. Two years ago.
Sarah-Jane was really the only companion that waited, who came back. Who stayed faithful. She decided to investigate things. Trying to find him. And when she finally did, she was disipointed to see that his companions were getting younger. And fighting with Rose. The Mrs. and the ex, as Micky had put it. He had to admit, he like how Mick put Rose as the Missus. Anyway, he still regrets leaving Sarah. He hurt her. Yet, 40? years later, she was still searching for him. And she still turned his offer down to travel with him again.
"Doctor, who was your companion?" Amy's voice shook him out of his reminisce. She walked over to him and wiped the tears off his face that he hadn't even realized had fallen.
"Sarah-Jane. Way back I left her...but 40 years later I found her again, and I had really hurt her. And she died of cancer," he explained. Rory walked over to him and awkwardly patted him on the back.
"Doctor, she probably lived a long and happy life, and is probably just happy to know that your safe...kinda...and happy."
He took in what Rory said, and it helped, but to think, never to see that smiling happy face again.
He started to sob for awhile, his head in his hands, and Rory and Amy stayed with him. They had never seen the Doctor cry like this.
When his crying started to subside, he got up and started to fiddle with the TARDIS console.
It was quiet for awhile. But then Amy broke it.
"Doctor...are you ok?"
"I'm always ok."
But in truth, he wasn't. He knew what Rory had said was true, but he would never see her again. Just like Rose and Donna and numerous other companions.
Sarah-Jane had died, and he hadn't even known.

The End
In loving memory of Elisabeth Sladen.

She died on Tuesday, April 19 of cancer at the age of 65.