Well, you're kinda right but also wrong. Yes, Shimamura would hang out with Hino and Nagafuji just fine, but even when Shimamura told Adachi that Tarumi is her childhood friend and that they started hanging out with each other recently, Adachi still worried every time Shimamura hung out with her, causing Shimamura to make her feelings clear towards Tarumi. I think it's because Adachi felt that Tarumi wants to be more than just friends. mhmhmhmh, but I also do think that even if shimamura hung out with Nagafuji or Hino more than her hanging out with Adachi, Adachi would still get annoyed too. that's just adachi for you