Honestly it could be as simple as "he is nice and is always helping me out and now i got too used to having him around and enjoy his company" and him just being "she is nice to me and really cute". I know people that got together at high school for similar and even weaker reasons and are still together almost 20 years later. Author has to at least show good chemistry. Two characters than dont really know each other yet being "perfect for each other" is one hell of a tired trope. Kinda boils down to bad writing tbh.
I think what rubs me wrong about the "I like them because they're nice to me" rationale is because it feels self-serving. That's just someone you want around because they make you feel good, or they do things that make life easier for you. That can certainly be enough, and it's not even indicative of a person's desire to "use" another. But it feels shallow, like she only likes him because he solves problems for her, but the moment he didn't or couldn't she'd lose interest, type thing.
Which dovetails into the "chemistry" facet you mentioned, yes--I just think there needs to be something more, that's built on who they are and what they mean to one another on a more fundamental level beyond "I like that he makes life easier for me" or "she's a senpai who is cute and nice (other than the apparent constant teasing/cajoling)".
Right now, she's a senpai who apparently gets a kick out of teasing him, which I would think does little to help his anxiety now that they're not together, and he's second-guessing and overthinking every moment he's around her while wanting to "stay away" but then going out of his way to prolong every interaction they have. Maybe that will transform into something more meaningful as the backstory fills out and we see more interactions, but he's so nerve-addled that I'm just struggling to understand what she actually sees in him outside of any utilitarian benefit. We're a mere two chapters in, so I will certainly allow for growth in the narrative and the character-driven dynamic between them, but two chapters doing the same "bit" right at the outset makes me wonder.
A really compelling development could be if he were bullied and basically peer pressured to dump her by envious classmates. I've also seen that irl and could be a good story to tell. Basically getting over bullying and peer pressure to realize thats just bullshit and desnt matter so go be happy with your girl. They both seem to be a good influence on each other, so the only realistic place the author has to explore is the reason why they broke up and how they mend those wounds.
(Please, author, don't let it just be the simple trope UdenEmpati said where nothing gets developed)
I'd be down if he were forced into it by jealous/upset classmates, yes. That would at least allow for him to have not
wanted to break up with her, and would mean that they both have an active desire to see something rekindle between them.
I'm not sure if that's the case, however, as I do feel like part of his internal monologue would have referenced that by this point. The FL wouldn't necessarily need to be aware of that sort of reason, as part of the stipulation imposed on him by those classmates could be that he breaks up, but that he "makes up a reason", or something, so that the FL isn't aware that it was jealous boys who pushed the ML into ending things. However,
we the readers wouldn't need that sort of information hidden from us, to keep the plot and premise compelling. Arguably, it'd be imperative to know--because as it stands, the ML seemingly embodies the very qualities that those classmates apparently decided meant he wasn't worthy of the FL.
And, he was in middle school for an entire year between that point and the start of this manga, while she had moved on to high school. So that's a year for him to figure himself out a bit, and instead he is seemingly as bad as he ever was when it comes to anxiety and awkwardness and so on.
So if he just overheard gossip/mean-spirited opinions from classmates and freaked out, thought to himself "she shouldn't be with me because she'll be hurt by what they say", and then broke up with her all on his own because of that....then I would be less enthused. There's still a story in there, potentially, of him coming to understand that he doesn't have to listen to or care about the opinions of others, and that
hers is more important than anyone's but his own. I don't like it as much, because he starts from an even worse place than he would otherwise, but it would represent growth on his part, which is what I ultimately care about.
But I mostly want more from
her side of things. Because right now, she's incredibly one-dimensional (he is too, but we also have his internal monologue & narration/side of past events). She's just the 'cool beautiful senpai' who spends every interaction with him in full on Teasing Mode, calling him a pervert while throwing herself at him, and is somehow apparently interested in him after a year-long separation
and after they'd broken up.
She's got looks, popularity, and is clearly "above" him in most metrics that school kids care about when appraising this stuff (him included, clearly), so her still being fixated on him needs one hell of a reason behind it--because as I said above, "he's nice and does things for me" really doesn't cut it.
That's not a boyfriend, that's a gofer, and
that would make for a godawful ending if they got back together on those grounds alone with nothing else from her side of things.