Not sure if this is the best place for this but I've just finished reading the book and found it desperately sad that after everything she wrote about and to Lenny in it that they separated. There is a fair bit mentioned about the incident with another woman, both directly and indirectly and anyone reading it at the time it was first released would think it had been dealt with and that they had moved on.
It doesn't look that way at all now, sadly. It made me wonder if 'it' (infidelity, whether emotional or actual) always finishes you off as a couple in the end? Of course, this may not be the reason that they ended their marriage but the incident got a lot of space in the book considering it happened over ten years before the book was written.