I even consider the first option as the probable one. If Josy was in a relationship with Zoey, there are several ways for DPC to place drama.
Example:
Zoey left to become a surfer. Maybe it was just a pretext because she wanted to avoid an unpleasant situation for her. She may have become more and more attracted to the MC and didn't know how to break it to Josy. She decided to get out of the way of both. Josy perhaps blamed Tommy for Zoey's departure. Maybe that made Josy hate Tommy. Now imagine the drama when Josy and the MC find out about all this.
Josy doesn't like Tommy because he's Tommy. That, and he's Monica's son, and Josy doesn't like Monica therefore she doesn't like Tommy.
It's really just that simple.
Zoey's reason is also likely to be just as simple; because she wanted to. Neither she nor the MC viewed what they had as anything more than FWB, so that's what made it easy for Zoey to leave but it was only after she left that the MC realised it wasn't right for him but he didn't he know if he was missing her as a romantic partner or a sexual partner, and that's the purpose she serves in this story, to give him that life lesson and that emotional experience.
MC thought to himself at Zoey's departure that there was more than friendship. He also had this pain in his chest like in EP1 with Josy. In retrospect, MC himself talked about Zoey having a friend with a big brother who buys them alcohol. Tommy would not have been of age at that time. But know that he has been using his FakeID for a while.
Again, in a town of any size, there's going to be plenty of people who have siblings that are old enough to buy alcohol and who would do so for their younger siblings. Her friend could be literally anyone she went to school with, which was, remember, a different school from the one Josy went to.
So Josy and Zoey don't have to be connected in any way and I think it is very unlikely that they will be.
"Just because they lived in the same town doesn't mean that Josy was the only person in the whole town who had an older brother who could buy alcohol." I agree. But they lived in the same town, that makes it possible.
Except for the fact that Josy deeply dislikes Tommy and she would never ask him to buy alcohol for them and he, being Tommy, probably wouldn't do it even if he had been asked.
The idea that Tommy would be the "brother" that Zoey spoke goes against so much logic and character depiction in this game that it makes it highly unlikely.