If she took Po as her husband, she would be making promises about a future she couldn't yet see. For once she became his wife, she would be his forever. And, no matter how much freedom Po gave her, she would always know that it was a gift. Her freedom would be not be her own; it would be Po's to give or to withhold. That he never would withhold it made no difference. If it did not come from her, it was not really hers.
For most of the process, nothing but faith, fueled by your own stubbornness, will be pulling you along. The work that you've done on the book so far won't be much comfort, because so much of it will be insufferable crap, until the very last moment, when you figure out how to fix it and everything comes together.