That little blue book. Blimey, Was that hard to get close to! To touch it was near impossible. River never let it out of her sight. The Doctor tried, of course, to steal it. He never got close enough to read anything in it. Not for a long, long time and anyway, most of his attempts at stealing it ended in a pathetic lie or a mumbled excuse or even, most times actually, sprawled flat on his back on the floor.
After what the Doctor saw as, military operations, River always had the book and the Doctor was right back where he started. Spoilerless.
There had been times when his attempts had been successful. Three times in total.
The first was when the Doctor was young. River still scared him then and he couldn't believe his luck that he had made it so far as to get close to her diary, let alone touch picked it up and weighed it in his hands, then looked around the empty console room and licked it as if that might give away anything. It didn't. He stared at it for a while then lifted the corner of the cover cautiously. A noise sounded from outside the console room and the diary was instantly flung across the glass floor in flight.
The second time the Doctor was brave. He knew River. Knew who she was and, to his own shock and surprise, had kissed her. Multiple Times!
This time, River had disappeared into the huge hall that was her wardrobe and had left her diary in the bedroom. He flicked through, passing stories he knew and finally stopping at one he didn't.
The neat writing made him comfortable for a reason he didn't understand and he sat on the bed as his eyes flicked over seemed innocent enough until he reached the words "bare skin". His own skin instantly had goosebumps but he continued anyway. His eyes gradually widened as he read on and, once again, before he reached the end, the book was flung across the room.
The third and final time, the diary was full. The Doctor visited the library often, only to sit and stare at the little blue book that had confused him for so long. It wasn't confusing anymore. It wasn't his future anymore. It was his past and Rivers past and all that was over now. He never read it until their wedding anniversary. Not the first anniversary and not the last either. Just one. But it was important. He was going to die and he wanted to read it. In this body. The body that had loved River and the body that she had loved back. The body that had run with her, through time and space.
He sat in the corner of The Library for hours. It could have been days. He didn't know. The pages were old and crumpled and ripped in parts but he was gentle with it. Like he had always tried to be with River. He read it in one go. Didn't stop for anything and, by the time he was finished, the writing was stained and distorted with small, salty teardrops.
This was their final goodbye and the end of their story.