It's a kind of relationship that doesn't need much words or any touchy declarations of any sorts. Jim and Sebastian have an understanding on a whole other level, mentally and physically. Sometimes it's just a look that gives Jim to understand that Sebastian isn't in the mood for his games, which, of course, does nothing to the fact that Jim will continue with whatever he is planning.
Later, though, it's Jim who places his hand on Sebastian's shoulder, maybe for a moment or just a quick brush of his fingers, but it holds a lot more meaning to it than anyone could ever understand.
It's the little things, a side glance or nothing at all that tells Sebastian whether Jim wants him to be there or not. Silent conversations that give each of them an idea, an exact example of what words the other might want to say but doesn't, because it's already been said.
One could call it love, but it's not that, it's more - it's entirely different. Love seems too small for what they have, it doesn't quite fit into the concept of what Sebastian Moran and Jim Moriarty are.
In the end, it comes all down to the point where it is truly fascinating that there's a person Jim allows to be this close, gives him glimpses of parts that no one's ever seen - maybe not even himself. Sebastian might not fully understand what's going on Jim's head, but he gets to learn and watch him in such a intimate and personal way that probably neither of them really expected to happen.
