Welcome to FAF!
And thank you for sharing your testimony here!
What a blessing to get to know you.
Near the end of your post, you asked,
"What was God's original plan for marriage?"
In my experience these number of years in exegeting Christian Polygamy, I have found that the "core" of your question here is often the "presupposition" which the anti-polygynists try to use, even though it's only their subjective view of it all. (I am not suggesting here that YOU made this "presupposition", but only bringing to your attention how most of us in Christian Polygamy who discuss these things with other Christians will, at one point or another, hear some anti-polygynist try to use this very "presupposition" of the "original" plan of God as at the garden of Eden. Indeed, perhaps, for all I know, maybe some anti-polygynist has indeed tried to use this "presupposition" on you, which could even be why you're asking this good question here. If so, I do pray that my reply here to you will be of at least some small help for you. :-) Namely, the "presupposition" the anti-polygynists try to use regarding the issue of "original" plan of God.
That is, What was God's "original" plan in all things, such as regarding marriage?
In all actuality, I would say that it is really irrelevant! :-)
the appearance of what we would perceive as being the "original" plan, as what we found happening in the garden of Eden,
that is what we are to then follow,
that would dictate that we are to likewise follow the apparent "original" plan that we all walk around completely nude, as did Adam and Eve.
After all, that was the "original" way God "planned" it!
But that concept would be absurd, of course. :-)
And so it is likewise pertaining to any apparent "original" plan pertaining to marriage.
© April 28, 2000, TRUTH BEARER
P.O. Box 765, O.O.B., ME 04064