I think it's because she knows deep down that he's already made up his mind and it's not the answer she wants it to be. He's stalling around giving her that answer because he is hoping she will come around to his way of thinking
That's what it sounds like to me.
Which is why I advise everyone take a break and time out all by themselves. So they can listen to the quiet inner voice. Get clear on what they are willing/not willing to do/accept. And find the courage to SPIT IT OUT.
Otherwise it is going around in circles like everyone is "No, YOU go first." Nobody wants to go first and own their own wants, needs, and limits. Everyone wants to go second and be all "What I want depends on what THEY want."
John seems to want a polyship with Lydia and Sarah, but does not seem to clearly want to articulate "end of monoship." He may or may not want it ALSO to mean end of marriage. But he seems fearful to state "I want end of monoship" because Lydia feels strongly about monoship. Has stated as much -- even up to it is divorce if she cannot have monoship or at least primaryship.
But I don't hear she's particularly enthused with that "hybrid option." If you can't go there with enthusiasm, don't bother. Throw that option out. That's why I put it grey. There is nothing wrong with wanting monoship!
Lydia gets to make a value call -- value being with John, even in polyship more? Or value monoship more? It's a call that is hers to make.
Otherwise time keeps on ticking by. And sooner or later another player explodes like Mike did/does from the pressure. Then that solves things another kind of way.
I feel for you Lydia -- but seriously. Take a time out. Decide what YOU want MOST here.
a) Your need to be comfortable and no longer "Ack!" feeling. The need to KNOW one way or another so you aren't hanging in the balance. (ex: You break up with John. There. Sucks, but suckage with an ending in sight so you can reach for your next happiness. No more "ack, hanging in balance feeling.")
b) your need to be in romantic relationship to John. (ex: then you serve hang time while he sorts his shit out. Even if it feels yucky. Give John a deadline to present you with his offer. THEN you listen and discuss the offer he brings you. You may or may not accept the offer. But at least you know the suckage of hang time has an end in sight. No offer by deadline? You check out toward your next future happiness. Walk away from drama crazymaking things.)
c) your need to be in monoship or at least primary in a "V" situation in a romance (You could choose to get real clear on this (with John or future partner) and do NOT swing again knowing that emotions can throw a monkeywrench in there. You have learned something about yourself in a swing situation. )
It's hard to feel. But options seems pretty straightforward to me.
1) You decide you are done and get out NOW and leave crazymaking behind you. You move it toward your next future.
2) You decide how much more you are willing to hang around waiting. Giving John to the end of November to give you an offer to consider is not unreasonable to me. Accept, adjust and accept, or decline offer -- and you leave crazymaking behind you regardless what you pick. You move it toward your next future.
Move it forward. Step away from the crazy.