Opposed Timelines

She knew that the time would come up.

River Song always knew that it was impossible for her to stay with her beloved Doctor. In the first time that she found him, she knew very little about him. (Only the as she was planned to do.) But he knew her name, knew her heart. The truth was that the Doctor to know more deeply that she herself. River was sure that this man was their present and future.

But with the passing of time, she realized that every event that occurred, she things she would know more about the Doctor, and fewer things the Doctor would know about her. They were in opposed timelines. It was a matter of time until the day comes that he does not know of her existence. That would be the end of the line, unfortunately, for her.

She knew that this could not be changed. Time can be rewritten, but not this time, not this line, she does not dare.

Shh Spoilers.