Hello Clara,
It has been a long time since I have talked to you. I wonder if you even remember. What has happened in your life? You're nearly 40 now, are you happy? Have you begun to accomplish your dreams? Did you meet someone new? I apologize. I shouldn't ask so many questions, I must be overwhelming you. I never should have left. The pain of losing her just tore me apart. I didn't even know how much she meant to me when I lost her either. My dear River. She met me too early. And now she's gone. And you're gone. And Amy. Rory. Martha. Donna. Rose. Everyone. I lost everyone. Pushed them all away or harmed them. I must be toxic. No matter how hard I try to save the world, in so many ways, in so many times. I put on a smile and a show. But I am hurting the world while I help it. I just wanted to tell you goodbye. My impossible girl. I'm out of regenerations. I think it is time for the world to save itself.
-The Doctor