Character A and Character B meet over the summer and have one of those sweet, passionate summer flings that ends as soon as it's time for each of them to go back to their regular lives. Sure, they could keep in touch, but they're both busy people with busy college lives, and deep down they know it's best to leave things as they are and cherish the memory of their short time together.
A has extra reason to want to focus on her school work this year: she's doing an exchange program with a different college, and she wants to impress her new professors. What she's absolutely not expecting is to run into B the second she walks into her first class.
Alternate flavors:
Tell me more, tell me more: much like Danny Zuko, B has a bit of a reputation on campus, and it doesn't match the B that A got to know over the summer. Which one is the real B? And will A still feel the same after finding out? [ OR: the Grease reboot ]
What happens at the beach stays at the beach: A is heartbroken to find out B is in a relationship when they meet again. She's even more heartbroken (and, let's face it, pissed off) when she finds out this is a very long term relationship, which makes A the other woman. What A doesn't know is B and her boyfriend are just best friends who have been pretend dating since high school to cover in front of their very homophobic families.
You have a what?: though B is thrilled to see A again and their summery feelings still exist during the fall, B doesn't seem to be interested in picking up where they left off over the summer or even to try and see where their feelings lead them. B lives off campus and always seems in a rush to leave after classes, and A is starting to think B is hiding something. As it turns out, A is right: B has a son/daughter, and after spending the summer break with their father they're now back home with B.