It is actually suggested several times that they have a physical relationship. I wasn't able to find a reference that suggests that they have sex, but here's one that certainly implies that they get physical:
https://dynasty-scans.com/chapters/a_room_for_two_ch56#4
Kasumi: You're going to be teaching? That's amazing!
Sakurako: As far as I can make out, I'll be tutoring...
Kasumi: HUH? You wanna make out? Doing it here is a little...
Sakurako: NO! I meant I'm going to be an assistant! I didn't say anything like that!
Then on the next page, Kasumi admits that she tends to not listen very closely and her head goes blank when she's hungry and she gets sleepy when she eats...
But Kasumi's reaction isn't one of shock that Sakurako would want to make out, but that they're in public, which suggests that making out in private isn't something that would be a problem and is probably a regular thing.
Then here:
https://dynasty-scans.com/chapters/a_room_for_two_ch56#7
When asked for love advice by one of her cram school students, Sakurako realizes she doesn't really have any experience with the whole 'does that person like me or not' aspect of love, because:
"Kasumi-chan and I were pretty lovey-dovey from the start... so I guess I've never had to worry about that stuff."
last edited at Nov 11, 2019 1:42PM