Some thoughts after catching up to the manga
First of all, if I'm being honest, Yamada slapping Sasaki because she was feeling overwhelmed feels very Kouji Seo like (iykyk). She could have handled it a little better, although she did ask Sasaki two times to reschedule their meetup.
Also I saw a lot of people saying that maybe the story is gearing towards a coming of age ending rather than them ending up together. Thing is I don't think it's gearing towards a coming of age ending.
See, first of all let's go back to Oono telling Sasaki her backstory. Of how she used to hangout with this policeman behind the supermarket. That story itself greatly mirrors Sasaki's and Yamada's current situation as to how they hang out. Now the thing is Oono could've completely skipped over this story and just told Sasaki she's retiring soon and all. But we need to remember that she's one of those characters who notices things more than the others. In an earlier chapter, she noticed something was off about Yamada and approached Sasaki about it.
So basically that means her backstory doesn't only exist to give her character some depth, she told it to Sasaki as a warning, that if he doesn't start being honest with Yamada soon, both of them might end up like her and the policeman. As for the empty cigarette box she gave him, which she held dear to her for so many years. She might've given it to him to serve as a reminder of the very same thing. Because she's retiring soon so she's not going to stay there much longer. But that cigarette box will serve as a constant reminder to him.
And I think Sasaki kind of did take that warning to heart. Because after that, when Yamada told him, he didn't need to drop her home anymore. He didn't just considerably step away. He directly told her he wanted to continue to drop her home and that he wanted that to be his responsibility. Usually in the past he has been considerate and kind towards her, this time he was direct with her about something he wanted. Also, Yamada's reaction to him saying that is a clear implication that she wanted the same thing too, but she knew he'll step away because of how kind and considerate he is. I think that particular moment is from when Sasaki has started becoming more honest about what he wants. So because of all these signs and all I do think the story is gearing up to them actually ending up together.