I tried yesterday afternoon to get us off the book and back to the OP, but apparently we're too far gone....
TLS2's original question, apart from the LL framing, expressed a concern re how she would continue to feel loved, based on her present understanding of how that works, with another woman in the family. TLS2, apart from all the "is too, is not" banter above, the basic answer is that it's not going to work the way you presently understand it.
A reasonable analogy is the only child. (Not a perfect analogy, but a reasonable one.) It is a well-known and rather unremarkable phenomenon that whenever parents have an additional child, there may (not always, but often) be some jealousy issues at first. Generally these tend to get smoothed out rather quickly, and everybody moves forward into the new family arrangement together. Sometimes there is no problem. Sometimes the problem takes longer to resolve, and occasionally lifelong sibling rivalry issues take root.
When there are no additional children, another well-known and equally unremarkable phenomenon is the general personality type of the only child. A little self-absorbed, let's say. Not because that child was born evil, but because it didn't go through the natural conditioning of having to share with siblings as a child.
Tying it all together: In the area of child rearing, most people that have children at all tend to have at least two or three, and the phenomenon of the only child is seen as an outlier, a way in which sibling-less children are actually in a sense deprived of normal (and normative) childhood experiences.
But what if 500 years ago, based on some bible verses that use singular nouns and pronouns (e.g., "train a up a child in the way he should go"), the church and civil government had agreed that having more than one child was unlawful? Today we would be conditioned to accept the relatively self-absorbed expectations of the only child as 'normal' (and normative), and we would not be able to imagine how it could be healthy for children to have to "share their parents' love".
In like manner, we are all operating from a set of cultural assumptions that are non-biblical at best, and typically more anti-biblical, when thinking about marriage. This must change.
TLS2, I apologize. I had two opportunities to start a new thread to discuss the stupid book, and then when I did try to rein it in it was too late. The answer above is the best reply I can give to your burning question. Your concern is reasonable and understandable, but ultimately it is a function of cultural conditioning (which includes pop Christian self-help books, but is so much more than that), and that conditioning is something we all have to overcome to make this work. (And by "this" I mean biblical marriage, not just polygamy.)
May God grant you patience and fortitude.
