Thank you for pointing me there, TigerEye.
This really resonated with me... . I think that is exactly what happened--the engulfment fear kicked in and he had to break up with me to abate it:
Often those with BPD will generate emotional chaos and conflict to create space, distance "other" in search of some temporary relief to engulfment fears which then quickly leaves the borderline feeling as if they have been or about to be abandoned. It's a classic no-win situation for the borderline and then of course by extension for the non borderline.