She prefered Adachi ? Or she chose her because it just so happens that Adachi was the first one to ask her out? What if it was Tarumi who confessed first, would Shimamura say yes?
Tarumi never had a chance to begin with. Shimamura outright thought that their friendship once failed because of Tarumi. Even if Shimamura didn't meet Adachi in highschool, she would've rejected Tarumi. Along with Gon, Adachi was one of the two who are precious to Shimamura and the only one who make her dull life more interesting. Iruma just wrote how Adachi and Shimamura are fated with each other. So basically, if Adachi didn't meet Shimamura in high school, they're gonna meet and fall for each other somewhere else. If Adachi didn't fall for Shimamura first, Shimamura is the one who gonna fall for Adachi first.