Warning! Spoilers ahead for Future State: Batman/Superman #2
As DC Comics' Future State comes to an end, so does the friendship of Batman and Superman. In the second issue of Future State: Batman/Superman, the Magistrate has occupied Gotham, and yet they've already become too dangerous for the Man of Steel. Because Batman becomes keenly aware of this fact before Superman truly grasps the danger the organization poses, conflict is created between the two heroes. Ultimately, this leads to Batman ending his partnership with Superman entirely.
In Future State: Batman/Superman #2 from writer Gene Luen Yang, penciler Ben Oliver, and inker Stephen Segovia, Batman is trying to find Superman, one of his only true friends and strongest allies outside of the Bat-Family. The Man of Steel had been taken hostage in the previous issue, due to his trusting nature. As a result, Superman was stabbed with a kryptonite knife and taken to Professor Pyg. The gruesome doctor is revealed to be an agent for the Magistrate, and Batman soon discovers that the organization has managed to weaponize Superman's DNA as a result, replicating his eyes (complete with super sight and laser vision) and inserting them into the city's vermin, thereby creating unsettling biological surveillance drones.
Additionally, Batman also finds that the Magistrate has figured out how to synthesize kryptonite, Superman's primary weakness. As soon as Superman manages to get free of the Magistrate's captivity and the two heroes get clear, Batman reveals to Superman all that he's learned, which he uses to conclude that the Man of Steel has become too much of a liability going forward. Despite Superman's desire to continue helping take down the Magistrate and for them to continue working together as they always have, Batman refuses and effectively ends their partnership.
Naturally, Superman is pretty frustrated by Batman's apparent lack of trust that Clark would be able to handle himself. However, he does tell the Dark Knight that he knows Batman can handle the Magistrate on his own, trusting that he'll make the right decisions. What Superman doesn't know is the deeper reason why Batman is refusing his help: Batman wants Clark to live, seeing the danger as too great of a risk and not wanting to lose him.
Thanks to Batman's internal dialogue, readers are able to see that Batman was significantly worried not just for Gotham's future, but also the danger the Magistrate poses to Superman. As such, the Dark Knight believed the only way to protect one of his greatest friends and keep him from getting killed was to end their friendship altogether. While it's a rather drastic choice (it's not like Superman hasn't faced the threat of kryptonite before), it seems as though the combined risk that would come to Gotham if Superman were to stay and help made up the Batman's mind. Despite the sad fact that the World's Finest ends in DC's Future State, at least it came from Batman's well-intentioned desire to keep his friend Superman safe.