leftword,
The sudden switch or turning is disconcerting to say the least, especially being so idealized, in most of our cases not long prior to a sudden and cruel discard. It feels as if everything prior was maybe a lie, yes?
Have you seen this, from the lessons at the top of the board?
10 Beliefs Than Can Keep You StuckOr the top level article:
https://www.bpdfamily.com/content/surviving-break-when-your-partner-has-borderline-personality#10While my ex was living a double life from our home, I read her journals, which she conspicuously kept out, not hidden. She lionized both her beau and me at the same time while telling me to my face that I failed. Her beau excited and validated her (due to her lack of self worth). We had 2 kids, 1 and 3 at the time.
Words and promises, in retrospect, couldn't be believed, and that was quite a shock, as I'm sure it is to you. Kind-of apologies came years later, and even those were self-centered because she was hurting and needed validation.
I'm with you on being concerned about a smear campaign. Engaging might feed the drama, however.