First off I'd just like to announce that I finally found out what the hell "Who Killed Cock Robin" is a reference to. Apparently it's an old nursery rhyme.
Second off, every time I read one of these traumatic updates and feel like my soul is being crushed, I come to the comments, see "Chekhov's Bear," and start laughing, so thank you. I'm not knocking the thought process behind it I just think it's a really funny phrase to see.
Finally, I keep having to remind myself that the very first scene in the manga seems to be set very much towards the end. While I can totally see some sort of "once this moment occurs in the normal sequence of things, it will be revealed that this isn't the end but is instead set before the end, and something unexpected will change the ending," I can assume that at some point Colin will be in shackles and will at least believe that she will never see Mary or their garden again.