Thanks for the feedback, guys. The problem isn't so much Zack being fickle about who he likes, it's the execution I've made that's the main issue, in my opinion. It's ok for him to be unsure, but the moment that he pulls both girls into his mess and kicks 'H' to the curb when he decides he wants 'V', that makes him a jerk (I've wrote that, and that's what bothers me).
He arrives at the cabin liking Victoria and then gets interested on Heather; as the days pass by, he unconsciously pursues both of them and makes them interested on him. In the space of a day, he makes out with Vicky in the kitchen, gets dumped by her thanks to a plan, gets Heather's hopes up by having a good time with her at the movies and the lookout point and then dumps her because of Vicky almost as soon as they get back, has sex with Hannah and decides he doesn't want Vicky anymore, finishing with a sudden interest on Ashley. That's the result of my indecision regarding the story, and that's what hurt both the story and Zack's character in my opinion.
But there are other reasons for a potential rewrite; the mystery of the bears and the hidden man, for example, I feel that I didn't execute this particular storyline as I originally intended; then there's the fact of Chloe and Gavin getting together too early and making them unavailable for other plots; Brandon and Ashley going for other people less than a day after breaking up a two-year relationship; the list goes on. All in all, I feel that the characters's personalities changed a lot with time since I first posted the story, but it isn't realistic in a time span of just six days inside the story.
I want to be able to write the whole story knowing what I know about them now, and go deep into each one of their heads to make their actions plausible. And most of all, start the story with all the pairings already set in stone, so I can develop each one properly, without the need of making the story a Frankenstein again because I changed my mind. It's very likely that I'll change a few details about their backgrounds as well, for example, Zack and Gavin not being too much alike, Zack and Ashley having a previous friendship (it always bothered me a lot that their sisters were best friends and they just befriended each other through Brandon), etc.