If this manga wouldn't be so cute/moe and never serious, you would think Kasumi and Sakurako are in a serious relationship. They are closer to each other than literally all shoujo ai manga couples i've ever seen. Since we already had a handful of kisses(never serious tho), only an open confession and sex is missing.
You can find all kinds of hints in multiple chapters they are attracted to each other. In this chapter for example, that whole thing about Sakurako liking Kasumis personal body scent, you must be damn intimate with her before being even able to sense it. And liking another persons body scent is even a further step of intimacy.
Would be great to have just one serious chapter about their romantic feelings towards each other. These two being soulmates seems like an understatement. 👀