I held off on reading this thread until I finished the book, and now I am so disappointed there are so few replies, because I need to hear everyone’s thoughts!
I read the two parts as alternate universes. In part one she has no son, she has affairs, she struggled with her scene in the play. In part two, she always had a son, her husband has the affair, she plays the scene to great acclaim.
But…. The play her “son” writes, about a woman who struggles with reality. Yeah, I really don’t know what I just read either.