BPD behavior change ....

How does a pwBPD suddenly stop most of the previous self destructive behavior, when suddenly into a new relationship?

Idealization.

Who told you it stops? A relationship is one of the biggest triggers there is.

Getting into a relationship doesn't stop a borderline's destructive habits. That comes from plenty of time put into therapy and actually utilizing the tools acquired from it.

He e-mailed me and told me how great he was doing, no stress....no incidences for the past 9 months!....Like I was causing all his stress. I of course said," great, I guess going to jail, having a felony over your head, moving into a dump, a pending divorce, selling the only home you'll ever own, debts going into collections, getting suspended form work, no promotion this year, having a butt ass ugly fat gf and pissing all over yourself every night when your drunk...counts as a great year? Well, I wish you more of the same!" .....Yes, I am angry- angry he acted like he loved me, angry he spent all our money having to have the "best" of everything and now acting happy with nothing! It makes me so mad that he wants to act like I caused all of his anxiety issues and that's why he went into the hospital and cut himself so often, went to jail and such....etc. etc...... So, yes, he hasn't changed per se.....maybe he is drinking more and when we were together I asked him not to because he became violent. Could that be the stress??? I just don't understand....