Aww, I hate doing this to them now!!!
Well, this is fun. In a way that's totally not fun. He still doesn't know why Spike and Ianto are still living next door, why they didn't just move to somewhere across the other side of the dome. (It doesn't occur to him that he could have moved too. Perhaps because somewhere deep inside he's never really stopped hoping that one day he can get back together with them, like he did the time before, and the time before that. When you're all immortal, there's no such thing as never, is there?)
His mouth tightens and his back stiffens as they both start walking down the corridor together, without speaking. Their footsteps seems to fall automatically into rhythm with each other, and he catches himself and deliberately breaks the rhythm.