First, one of the most observant men in the world thought John was flirting with him. Now, the most observant woman in the world thinks John is in love with Sherlock, just like she is, in defiance of sexual orientation. Look at us both. Neither of us are interested in men, yet we both want this one.
The evidence is stacking up against you, John.
I like to think of this moment as a turning point, because he doesn’t deny it again after this. I mean, they’re still not a couple to way people think they are. But they might as well be, at this point. They’re a couple for all intents and purposes. No one means more to John than Sherlock does. They share flat, they sometimes share a room, they’re joined at the hip, and John loves Sherlock. And Sherlock loves John.
Irene is the one who must be jealous. John is the one Sherlock’s chosen. John is the one Sherlock talks to, even if he isn’t there. Sherlock always gets the last word, John says; their conversation never ends, but Irene can’t get one started. Sherlock sends John texts beckoning him, sends him texts when he goes for a walk on the moor, follows him wherever he goes. Irene’s texts go unanswered. John’s the one Sherlock has dinner with, in the end, even when he’s not hungry.
Irene turns out to be far more morally ambiguous than Sherlock is, heavily leaning toward the evil side even as she isn’t strictly evil herself. She’s willing to play with Moriarty if it serves her interests, in spite of the fact that he’s vicious and doesn’t care who will get hurt along the way. Innocent victims are his bread and butter. Irene doesn’t seem to mind that. Sherlock doesn’t mind either, per se, but he strives to prevent innocent victimhood all the same, not to participate in it. Irene choses to participate in chaos while Sherlock always choses to turn chaos back into order. Devil on the side of the angels? Perhaps. Irene is most definitely not on the side of the angels.
Knowing that Sherlock loves John, and that John loves Sherlock, she makes an extremely agressive play for Sherlock anyway. She knows what she’s disrupting. She knows she’s making john jealous and uncomfortable. She takes what she wants, that one. Or she tries to. She’s not even shy about it, not in the least.
Man, I love Irene.
Look at us both. Yes, indeed. She’s right: it’s a useful comparison. Sherlock isn’t interested in getting into bed with moral ambiguity, literally or figuratively. He’s got John, his north star of moral principle. Irene kisses Sherlock on the same spot John punches him: both of those actions are performed with love. And Sherlock, being Sherlock, chooses the straight forward punch over the complicated kiss.