That discussion repeats itself daily...Yeah, you cant blame her for turning him down because he was younger, but she made a joke out of it and laughed about it with her friends which hurt the MC, I would say she played a big part in ending the friendship, she could have let him down easily
Let's just say the MCs memory might be playing tricks on him.
More importantly they were teenagers, mistakes were made, years have passed... it's time to move on.