WARNING: The following article contains spoilers for Chapter 126 of Attack on Titan by Hajime Isayama, Dezi Sienty and Alex Ko Ransom, available in English from Kodansha now.
Attack on Titan isn't known for its sweeping romances -- its cannibalism and genocide pledges are kind of mood killers. However, other than Ymir and Historia's unrequited yearning for one another, one of the manga and anime's key relationships has always been the also unrequited one between Eren and Mikasa.
The pair are the very definition of "It's Complicated." Not only were they sort of raised as brother and sister (with no blood relation,) but the drama-filled nature of both of their family histories has been driving a wedge between them for some time in the manga. If Chapter 126 is any indicator, Mikasa could even be done with the man she's been one-sidedly obsessing over her entire life for good. If this turns out to indeed be the case, then this seismic shift will be a real rug-pulling moment for readers.
The scene in question has Mikasa visiting Louise, a young cadet whose military career was inspired by her idolization of Mikasa, in a temporary hospital following the "rumbling." She notices the injured girl has Mikasa's abandoned scarf around her neck. The scarf, as fans know, was wrapped around Mikasa's neck by Eren when they first met as kids, and until recently, Mikasa was never seen without it. It became a symbol of her devotion to the young boy who stepped in to save her from an abusive home.
Louise explains that Eren told her to throw it away, but she kept it instead. Mikasa regards the girl coldly before demanding that she give the scarf back to her. "I became a soldier because I admired you," Louise calls after her. "I have no regrets, because I chased after you... as I lived... devoting my heart."
The last we see of the scarf is it clenched in Mikasa's hand. She's not wearing it later on in the chapter, so it's unclear what happened to it. What is clear, is that Louise is supposed to be a mirror for Mikasa's feelings towards Eren, and so confronting Mikasa with a reflection of her own perhaps, pitiable, dependency has been a final wake-up call.
As soon as the time jump happened after "The Return of Shiganshina" arc, it was clear that Mikasa and Eren -- now into their late teens -- were already growing in opposite directions. Eren's rash decisions were made without consulting his closest friends. Although Mikasa begrudgingly went along with them, things took an unexpectedly nasty turn when he staged his split from the military in order to stop Zeke. To shore up his traitorous charade, Eren told Mikasa the "truth" in Chapter 112: That he'd secretly always "hated" her and that her Ackerman blood was what made her doggishly loyal to protecting him because her lineage compels her to, not, in fact, because she harbored real feelings towards him.
The pair haven't crossed paths again since, nor has Mikasa been in possession of the scarf. If Mikasa had put the scarf back around her neck, we could argue that she'd decided to believe Eren's cruelty really was part of his deception and forgiven him. But, the fact she decided to take it back and isn't wearing it speaks volumes. Assuming she hasn't destroyed it, as Eren suggested Louise do, she may still have it on her person in the hopes of resolving things with her estranged adoptive brother. Given his villainous turn, this might be tricky, to say the least. However, the scarf no longer being wrapped, tied in place, around her neck indicates that simply patching things up might not be enough for them to ever fully recover what has been lost.