Can anyone shed some light on this?
If you have been involved with a person with Borderline personality disorder, you have been mirrored in order to fulfill a sense of wholeness. Borderlines are part time objects, and they fulfill a need to make themselves whole by mirroring the good in others. When the relationship works, the feelings of wholeness are also egocentric to the partner's needs. When the relationship goes bad (as it often does) the egocentric injury causes the partner to split off the good part time partner (the BPD) and see them as bad in order to protect the ego. This is called the paranoid/schizoid position.
The paranoid/schizoid position is the response to the loss of the part time object that once felt whole- and it protects the ego from feeling badly (persecuted) by casting off and projecting the bad part time self onto the ex. It is a protective measure.
Splitting allows good to stay separate from bad. Projection is an attempt to eject the bad in order to control through omnipotent mastery. Splitting is never fully effective, according to Melanie Klein, as the ego tends towards integration of the part time selves into a whole again. This realization of good and bad in the same object causes depression.
The splitting and part object relations that characterized the paranoid/schizoid phase are succeeded by the capacity to perceive that the other (BPD) who frustrates is also the one who gratifies. Schizoid (hermit-like) defenses will remain, but feelings of guilt, grief, and the desire for reparation gain dominance in the developing mind.
“Before the depressive position, a good object is not in any way the same thing as a bad object. It is only in the depressive position that polar qualities can be seen as different aspects of the same object." ~Grotstein
Entering into the abandonment depression and coming out the other side means that you will need to find both good and bad in your failed relationship without returning to resuscitate and re-live it to seek good only. Coming to terms with the abandonment depression that good and bad are found- is your goal. Remaining in the paranoid/schizoid state is the ego's way of preventing the depression to occur. Given time and with no contact, it should happen. Keeping your Ex alive as a stalker persona (bad object) only prevents the bad feelings about yourself to arise. Give yourself a way to self soothe and let the feelings up to the surface and let them go.