The first time Jim starts describing a part of the day back to Sebastian- who had, of course, been there- Sebastian interrupts with "I know, boss. I was there" and Jim punches him, square in the jaw, and Seb can feel the bones unhinge a bit. Jim's sulky for a few days, and if Sebastian hadn't given up any hope of ever understanding Moriarty's mind a long time ago, it might have been confusing.
But Moran is one who learns from his mistakes- because in the desert and in the jungle one mistake is sometimes more than you get- so the second time Jim begins his description, he just grunts non-committally and continues reading the newspaper. Jim stops after about a minute, which makes Sebastian look up, and their eyes meet. Jim looks annoyed, as he always does when ignored, but underneath the annoyance is what looks like desperation, frustration, and what could be sadness. He throws knives into the wall of his study for three hours and sleeps curled on the floor.
So the third time, Sebastian listens, but it still makes no sense to him, the purpose of this exercise. He was there, he knows what happened, and he can't see why Moriarty would be on the verge of poetics about it. When Jim's finished his description, and there's no reaction, the look on Jim's face is obviously one of disappointment- but with oh there's why some of the futile longing that Sebastian recognises all too well from his own gazes.
And he isn't stupid, unlike everyone seems to think- and it's hard to blame them, because next to the harsh, sharp brilliance of Moriarty's mind, his own is dull and dim- so he gets it this time, what Jim has been trying to say with all of this. Because the descriptions, with this look and the earlier hate-filled silence, all of that meant-
He'd have seen Sebastian looking (how could he have missed it a mind like that) but the sexuality of the most dangerous man in London wasn't really a topic that was open for discussion, and the sniper had assumed from the complete lack of response that Jim was in no way interested, wouldn't give this little crush enough attention to mock it. So if his eyes lingered a bit too long on his boss's slim form or if he had to bite his tongue until it bled before answering when the Dublin lilt came out in an order- well, that was his own problem.
But Jim's stories, the pictures he paints with words Sebastian can sometimes barely follow- a sniper on the roof; the muffled sound of a shot; the slump of the target; the concerned cries of passers-by, small by the time they reach the rooftop; the sting of smoke from a post-kill cigarette; the careful, almost reverent way he takes apart and packs up his gun- all seem to say, in their own roundabout way, "Here is how you look from my eyes, here is how the world looks to my mind, please, join me in here for just a moment. My mind is brilliant and beautiful but lonely and sometimes too sharp. Please." (and Jim never says please)
They all say that Jim has wanted too, but not in the heated, lusty, animal way of his soldier. His desire was much colder, harsher, mathematical, dissecting. To touch and be touched, on anything other than absolutely his own terms- that would feel like being caged, choked, would remind him that he was still physical and trapped, in so many ways nothing more than a man. These brief glimpses into his glass-shard mind are the most he can manage, and even they feel too intimate.
Jim has watched the look of comprehension dawn on Seb's face, then change to a muted sadness at what it meant, for himself, for Jim, for a yet non-existent but hoped-for "them," of one definition or another. He walks over and settles himself as near as he can to Sebastian without actually touching.
Then Jim kisses him, hard and sharp with teeth and blood. One hand is pulling Seb's hair painfully and the other holds his wrists in place. There is nothing Sebastian wants more than to push back into that kiss, to bring their bodies close and take and take and take everything he has every dreamed of taking- but he's still a soldier, and he recognizes an order when he gets one, and the grip on his wrists is an order, a warning, though he could, stronger of the two, break it so easily- but Jim could break him.
Jim pulls himself away abruptly and completely, and Sebastian is grateful that he has enough self-control to not try to follow. After a moment though, Jim reaches over and digs his nails into the far side of Seb's neck, leaving tiny crescent-shaped cuts, and they sit like that for a while, in silence. And Sebastian wonders if affection and possession and obsession are really all that different, when you get down to it.