I am a little confused. How can you be an undiagnosed "BPD". Either one has had a professional administer something like an MMPI (or the like) and spent ample time in therapy coming up with it. BPD is one of the most misdiagnosed disorders. The reason why this matters is that if one or both of you falsely believes he has bpd (or your perception of what that is), then your relationship problems could stem from unheazlthy self fulfilling prophesies.

That said, my standard recommendation is to read a book called "I hate you, don't leave me. Understanding the borderline personality." This book has a section dedicated to learning to communicate with a person with mood swings. In your brief sentence, you said two things. "I am a SUCCESSFUL 40 something woman" and "everything is a competition". If you went to counseling, I would make sure that these two dots were explored for a connection.

I am a believer that every divorce disadvantages the children. Statisics support my beliefs. But to each person unto their own definition of "messed up". You could simply change your hopes for your children from "I hope they achieve a masters degree" to "I hope they don't go to prison for bank robbery" and you will increase your chances of them achieving your hopes.

Peace and good luck.