I feel like one of the promise is to get married. idk I feel like that's a common cliche when 2 characters are children and they typically make promise to be married in the future. will they actually get/show married, probably not but i feel like they will start dating and kind of end this series in a happy way. but who knows, i'd be great if they do get married and show it on here. Also, although there isn't a drama tag on here, i still feel like there will be character (guy) who will try and get at the FMC, but ofc it won't work since she likes the MC. With that being said, i feel like the guy won't cause trouble. She's gonna probably say "there's someone else I love," and the guy is going to figure out who and then leave and go towards him saying "you're lucky blah blah blah" and ofc the Mc wont understand what he means so the guy will probably say "your really dense huh," and just leave. So basically someone who will push them a bit closer, but that's just my speculation, don't actually think this will happen.
edit: i don't think he's that dense more so he knows not to get his hope high bc the FMC is basically in a higher league than him and he probably doesn't want to assume she likes someone like him.