I couldn't do it. I couldn't leave him, not again. I looked at John Watson and my thoughts started running at lightning speed, I could feel the tears welling up behind my eyes knowing I'd never see him again, the man who reminded me that I was human, by being my best friend and not giving up on me. My strange overwhelming urge was to hug him and tell him all that, that he was the bravest and kindest man I'd ever met, that I loved him more than anyone else in the world. But hugging him would definitely make me cry and if that happened, I'd never leave, I'd fight to stay and I couldn't stay. I looked straight into his face and saw everything we'd ever been though together, knew I'd be dead in six months- Mycroft never got these things wrong. And this was the last time I'd ever see him, there was no getting round that, I'd be actually dead, I wouldn't be coming back this time. And that made my eyes sting with tears that would cascade out if I put my arms round John Watson, my best friend and the best person in the world, it will break him and break me. I can't do that, I have to go, now, or I'll just keep running and people will be in danger.
All these thoughts run through my mind in a split second and I hold out my hand. John looks bemused; I know I would be in his position. I can't even remember what I said to him, probably something about the best of times, something with no emotional strings. And I walk away from him, the fantastic human being who made me feel like I was worth something, and I was saying goodbye for the very last time. The tears pool in my eyes, I'm weak and foolish because John makes me so. Sentiment is a defect found in the losing side, and I am on the losing side. I've lost him, I've lost everything.