Zoey "But also, you're friends with [name]. Hooking up with someone he's close to, I would never do that to him."
This is the only thing that matters and has weight in this dispute, how openly a certain character declares his intentions and attitudes and what exactly he/she says.
Zoey says that she wouldn't hook up with MCs friends (DIKs) or he is close to. This also means and includes girls and MCs LI as well and ruins some people fantasies about 3-somes with Zoey, etc. She is not THAT type.
Same goes for 3-somes with Sage (on her branch). I doubt very much it could be a J&M in such case, it seems very clear that 3-somes option for Sage would be among SGs only, and probably between ones, that haven't their own paths (Camila, for first). But on the contrary, Sage is the best option for 4-some on the J&M branch. Such scenes must be a path/branch specific. 3/4-somes can't be just an "optional" ones, there's too much effort and time consuming thing and work on to offer it as an option, while option usually also includes choice between something, rather than just accept or decline it. It depends on consequences, of course, so if they are negative, player should be able to decline it in advance.
Zoey may (and will) regret that she didn't tell about her feelings and emotions in time, but she clearly will not hook up with someone from the DIKs and at the same time remain/pretend a friend of the MC. 2 factors at a time. She values the MC friendship AND she doesn't want to hook up or get too close to someone MC is friends with. Her words and personality. And don't tell me that TC will convey ANY girl to cheat/to break their words and do something finally with MC if he just ask about it. Being implemented this will create almost unlimited branching, so it's quite impossible. There will be some specific girls and scenarios for this thing to play out, but Zoey doesn't look like an option here. I had a different opinion about her before episode 10, but the scene with Jacob changed my mind significantly.
And that's why her reaction when MC tells Jacob that he doesn't mind is so painful. She did not expect that MC wouldn't care and that he would be comfortable (and to be fair, MC is also not comfortable with this thought internally). And it doesn't look like a reasonable way to get rid of her. Rather, on the contrary, this is a very bad option, imo.
She takes the information much more calmly that MC already has a girlfriend (if he is with someone from MG) in the diary scene. And I don't see a scenario where she would try to make MC change his mind or that she would do something to spite him in order to get him back. It's not compatible with friendship and everything she's talked about before. But she won't mind to become a "backup" option if MC relationship goes south for some reason. Sage told MC about the same, btw.