I feel it wasn't so much that they're holding a grudge, but rather felt embarrassed about the way they shunned her back then. It ain't easy to look someone in the eye when you know you've treated them badly.
Can we talk about how the author just drew a direct parallel between Mako's feelings for Yoshida and Sachi's crush on Tomoki? That's like... almost a plain text confirmation that Mako is gay for the delinquent!
I mean, I know we pretty much knew that already, but still!