I don't get the upset over Zoey leaving.
Best friends drift apart.
Unless Zoey planned on marrying the mc, she didn't need to stick by him forever (and even marriage never guarantees that shit).
She always dreamed of surfing, was pretending to surf since she was little, and when her gran died, it nudged her along a bit more.
Although the departure stung a bit, for both of them, big deal. It wasn't meant to be goodbye forever. She was just getting ahead of him, she figured they be back together again once he finished school:
Sure she was a little selfish, but what the fuck, you put your own life on hold because you don't want your friends to miss you?
So she followed her heart, or so she thought, but it turned to shit.
People move to new towns all the time, they say goodbye to their close friends, keep in contact where they can, and sometimes just drift apart.
It's life.
But now she's back, and obviously, if she thinks things will go back the way they were, she's wrong, and that's just part of the story, and it could make for some fun situations.