How can I tell the difference between extinction burst and plain disregulation?
An extinction burst is a form of escalated dysregulation. It happens when the pwBPD does not get the desired response from the non.
Extinction Burst - The term extinction burst describes the phenomena of behavior temporarily getting worse, not better, when the reinforcement stops.
He keeps insisting that he's upset because my actions hurt him deeply because of his past, ( his mom is BPD) and it's just not that he didn't get his own way. I didn't give in, so I'm untrustworthy. Is it possible that he really believes that or is that just manipulation?
It is very unlikely that he would admit that the dysregulation is because you maintained your boundary.
There is no real way of knowing what he truly believes. We do know that the reality of people who present BPD traits is often created by their emotions. So, he could truly believe those things
in the moment. But, emotions change and that means that the reality changes. This is why it is advisable not to take things personally.
Also, today he calmed down and no longer wants to move out. Is this a recycle? Is this a good opportunity for more boundaries if I let him stay?
I'm not sure that I would call it a "recycle." This is partly because I dislike the term, but mainly because it sounds like he's starting to self-soothe. You've changed the dynamic, so the response to the situation changes.
What he may or may not be doing shouldn't be of paramount importance to you. I only point it out so that you can be prepared and make your choices accordingly.
What you do, how you choose to respond, and what you want should be where
the focus is. How do you feel about all of this?