As I write this, I am looking at your parents as they sit together on the stairs of the control room, talking silently, lost in their own little world that is considerably safer than the reality of TARDIS life. They look so wrapped up in one another that world war nine could have broken out and they wouldn't have even notice.
Your mother and father have always had something funny about them. Apart from the fact that your dad is thousands of years old and your mother grew up with a time rift in her bedroom wall, they just seem so in love and entwined with one another that it can't be humanly possible, or even possible in any other species.
How can someone be that in love and still have room for other people in their heart? Your mother tells me that I am her best friend, and she looks at me, telling me that I have a space in her heart right alongside you, my dear.
You and your father are her world and she can still love everyone else in her life.
I don't know how to say this, River. I've said it before, but it never really meant anything. Somehow, I just can't find the right words to say it. There has only been one other time that I have said it, but this time, it will mean something, finally.
See, River, before you, I could see. There was dark, but there were so many stars. The stars of my friends that lighted my night sky, and then a girl came along and she lit up the sky as a beautiful moon, filling the black. But then, you came, and my whole sky was alight with fire and reason that only you, my dear, could provide. You blazed through my life and still light a fire deep in both of my beating hearts.
You are wonderful. You changed time, were willing to deteriorate the whole of time just to save my life because you fell in love with me. You gave me all your remaining regenerations to bring me back to life and then you... No, sorry, spoilers. You'll just have to wait.
Jail is a cold and lonely place. Between you and me, believe me; I know what it's like. I sneak you out on some nights when I miss you too terribly for words, so I whisk you off to a different planet or another time zone because I know you enjoy the adventure and the thrill of it all, just like your lovey-dovey parents that have just started snogging. Yes, they do it right in front of my eyes that were made just for you.
Yes, I know what I said in the timeline that never happened. I told you that I didn't want to marry you. My dear, that was the single biggest lie I've ever told, and, wife, I am so sorry if I hurt you by saying such a horrible, untrue thing. You're my wife, and I am so glad that you are, because...
River, I wrote this letter for a reason, and there is one simple reason, but I don't know how to say it.
If I said it in front of your parents, it would just embarrass me, so that's why I put in one extremely long letter from my hearts.
Honey, I'm home when I'm with you, so I figured that I should come out and say it because I know that when I say it, I will mean it more than anything else I have ever said.
The Doctor xx
P.S. I love you, River.