Headcanon: Sherlock.
I don't think anyone really understands how obsessed Jim is with Sherlock. I mean he's really all he thinks about aside when he tries to focus on work or his math. I am not saying Jim loves Sherlock in a kissing and sex kind of way (though I think if Sherlock was to express he wanted that Jim wouldn't say no.) But that he feel Sherlock is the only one in the world that understands him-- that has to understand him. It frustrates Jim when Sherlock doesn't understand one of his puzzles. Because of all the years Jim has been alive he never met anyone like Sherlock. Sherlock is Jim's only distraction. His problem. He can't get him out of his head and feels he needs to be rid of him- but also like he wants to keep playing with him becase once Sherlock is gone- things go back to teh way it was. And that is something Jim doesn't want. He doesn't want to be alone.
Okay rant over.