Sage has said it all. Keeping your ex-girlfriend around is disrespectful and that's it. If the MC rejects Zoey in EP.11 I hope she stays away the same way Quinn stays away from CHICK MC.
Take the L, Zoey!
Aren't all the girls in this group technically exs? Zoey & MC weren't official. Despite spending relationship time together. But in one playthrough, you can date all five women & choose one (or two). The only one you wouldn't have done anything sexual with if not chosen would be Jill.
I don't think it makes sense for Sage to be upset with Zoey spending time with MC, but okay with Josy & Maya spending time with him. Josy was inconsolable after being told he chose someone else. How is Zoey a bigger threat than Josy? Jill & MC cried on a bench for an hour after he told her it was over. Why is she not a threat to his relationship?
To this point Sage is unaware of Zoey's confession. All she is aware of is Zoey & MC were fuck buddies (just like Sage could have been) since either middle school or high school. Depending on the timeline.