yikes thats hard for me
None of this is easy Corraline, but you are wise to be here, reading and posting. That's a great start.
The challenge for each of us is to detach from the other person, to the point where it does not matter if xBPD is with someone else.
What you are experiencing is normal. I, for one, wondered to the point of near madness how & when I had been replaced. Ultimately, it served no purpose.
I am still in the process of "unhooking" myself from the r/s. And this community has been a big help. I'm slowly, but surely, feeling compassion for myself.
I try to use my imagination to visualize a world where I am free and on my own. It takes time, but you're off to a good start by joining this community.