Answer was per my expectations.
C'mon guys here. What else was to be expected?
When has any woman choosen man after listening to his logical speech? Never. I'm certain many had gotten bored and were thinking: "What to say to avoid offending boring man, while saving myself from boredom for life".
Anyway, "seduction community" has already figured out formulas for having threesomes and multiple girlfriends who know each other.
Your vibe she could be accepting is because you could sense her attraction for you. Did you decided to build even more attraction? No, you wrote 15-page paper.
Anyone who expected otherwise must for homeword read again @Eristophanes epic in full:
UntoldGlory Trigger Warning: Epic Long Posts Ahead. This has kind of been bubbling its way to the surface, not so much in response, but as a result of some of the recent posts and comments over the past 6 months or so. Ginny's "Letter From The Front Lines" finally got me going. Samuel...
biblicalfamilies.org
Lesson not learned: Attraction is neeeded for marriage and even more attraction for plural marriage. How to increase attraction? Again epic has good model.
Proper approach would be to keep raising her attraction, starting using touch and avoid polygamy talk.
Touch is needed because ts signals preference for sexual relationship. I don't mean hug at start and end of time together. More than that.
She would start thinking about you in sexual way which would get her thinking about sharing.
Regarding polygamy talk most you should do is throw one/two jokes about you just to plant idea in her head. It could take several months for this to grow. You had gone to fast.
When she becomes interested in sharing, she would first check with your wife.
Anyway, situation can be salvaged. Shut up about polygamy, spend time together and instead of writing papers figure out how to increase touching.