They're still very much together.
What this chapter emphasises is... When you're in a relationship for a long time, sometimes you still feel the flutter and blush moments, but for the majority of it, you've grown so used to being with each other that you end up taking things for granted. Think of how you behave with your family, or how people usually do - it's "normalized". That's what Shimon says, that he assumed she'll always be there. But when Kie runs off, he's panicking, and that's when it hits him that things can actually change at any time. Whether it's hurting someone unintentionally, or someone getting injured, or work changes to accomodate, there are too many unpredictables out there. He's thinking back to the tiny moments that made their life special, like that candy, which become precious reminders over time that you have someone close enough beside you that you can share such moments with. But with a couple like these two, something like this is most likely gonna happen, over and over.. like it's mentioned in Shimon & Momoya's conversation.. but you grow closer because you can have these honest fights too and realise you need to appreciate and listen to the other person more. That's how you grow together and support each other. Kie also wasn't thinking of a breakup. It didn't even occur to her. But honestly, I think she should be appreciating Shimon more too.