I get where you're coming from, and I agree with most of your concerns, I have some over how DPC will present her, too, I really hope he does it slowly, not with a 'boom', pretty sure he won't actually, it wouldn't make sense.
dalli_x earlier brought great points I think, about how much they know each other, they both know how they react, they've been cut from each other for about 4-6 months, and there was a big misunderstanding on top of that (2 in fact, one where Emma shared the picture of Zoey accusing her of getting her boyfriend, and the other Zoey thinking the MC didn't want to speak with her anymore because he didn't reply, he was in pain, and probably met Josy by the time), but other than that they were together, all the time, for years before that.
While I hope a relationship won't be forced unto the MC (that would be increasingly bad writing), Zoey could remain an option (for later, not right in Ep9, wouldn't make sense either) while keeping an eye on the MC whenever he's around. And, the LI he pursued, who don't know him anywhere near as much as Zoey does, will be jealous of their natural affinity, which will cause some drama, good one I think, cause Zoey probably will see MCs reactions to said LIs if she happen to meet them. And since, as far as I remember, only Bella knows about Zoey, she'd probably be the one who'd freak out the most in such a situation.
Overall, yeah, their relationship wasn't clear, but I think it was meant that way, they didn't know what they were doing, or what they were to each other, they were too young, and shit happened. MC learned a lot, like you said, since Zoey's departure, but Zoey coming back, he probably will be able to put in words what he never could before, same with Zoey actually, the whole Emma/Bret discussion will come into play.