It's all going so well, their easy camaraderie spilling over into so many nights in front of reality tv and weekends at the park. There's all the shared laughs over his cooking and the thousands of photos on his fancy new camera. There's law books abandoned on her kitchen counter and Jesse's toys down his couch cushions. And it's simple, and maybe close to perfect. Until it isn't.
Until one morning when suddenly her digs are a little too harsh and the dinner invites stop coming. Their work is as slick as ever but she refuses to meet his eye and he notices Fin following their interactions discreetly. Every time his phone buzzes, "Rollins" flashing on the screen, he feels a moment of hope, quickly dashed when he notices the "Kim" where the "Amanda" should be.
He watches her over his coffee cup and acknowledges the strange weight in his gut; he misses her. He misses Jesse, and Frannie, and all the nice old ladies who comment on their "family" as they meander around on Sundays, all the nice old ladies they are too polite to correct, all the comments they blush and pretend to mishear.
...
Kim has been texting him non-stop for days and his desperation for insight into their little world spills out into their messages. It all comes to a boil one night at the little pub behind the precinct. Kim's there, thought she would surprise her sister apparently, though she's avoiding Fin like the plague and her hand on Carisi's arm says otherwise. Not that he notices. He's watching the door, waiting for that tell-tale streak of blonde.
And he catches it. She's barely a step in when her eyes find his, and he can see them catalogue his askew tie and ruffled hair with a fond quirk of the lips before her face shuts down again. Fin's discarded his beer, making his way quickly to her in anticipation, the only one aware of impending disaster. And that's the moment, as Amanda glances from Fin back to Carisi that she notices the girl standing just a little too close to him, the girl with matching hair to hers and a jumper right out of her closet.
He can't name the expression on her face, he's not sure he'd ever want to, but as she turns quickly on her heel he catches the new draw in her shoulders and the momentary wordless exchange between the new Sergeant and herself. He feels rather than hears the door slam behind her.
But he loves her, in some way he has not begun to dissect, so of course he is chasing her down the alley, calling out her name. And her agitated hands flying around her are not lost on him, the pace in her gait as she imposes and withdraws around him. He doesn't get any explanations but when she leaves with an exhausted "damn it Sonny", he knows that somehow this is on him.
...
It's Fin in the end who comes clean, or rather who hands him a sealed case file with a "you didn't get this from me" and disappears into the night. The pieces start to fall together, and every reluctance of hers he's ever fought about her sister suddenly seems a gross disloyalty.
When he shows up at her apartment he can only muster a humble "I didn't know", which she counters with a quiet "I didn't tell you". She pushes the door opened further for him.