She said she wasn’t expecting me to take to it as quickly as I did.
So she wants to stop because you transitioned better than she expected? What was she really wanting to happen instead?
Do you want to end your other relationships? Yes or no?
Do you want to try compromise like "Ok, no NEW people will be added. I will limit myself to those already here."
If she's only up for totally Closed monogamy where it is just you and her? That's the offer on the table? She's done with poly and she wants to practice that now? You have to decide if you are up for that. Or not.
If it is that she simply wants to end everything but is struggling on how to say it? Ask her. If she prefers to just let it ALL go and part ways amicably.
If you guys don't see eye to eye.... probably best NOT to get married. Def don't get married until this is well sorted out.
I’m willing to do whatever it takes to get Starbucks and I back on track.
What makes you think this is not the right track? She's already postponed wedding once.
It's not a terrible thing to be Engaged and have all the talks and find out that you are not
Deeply Compatible after all. To me? It's been a successful engagement period that spares you both the cost of wedding & divorce. As well as the emotional and mental pain. Nobody should enter a marriage in bad faith or with their heart not really in it. What for?
It's not a successful engagement like "Ok, we ARE Deeply Compatible. We are ending the Engagement Period and moving on to setting a wedding date." But it is still a success. That's what the Engagement Period is FOR -- the deep thinking/talks.
I hate to see you bending yourself into pretzels if this is about her not really wanting to get married or do poly.
Why force it? If her heart is not in either one any more? It's kinder to set her free. Are you willing to do that? Since you are willing to do anything to get back into right relationship with Starbucks?