This will probably be a long post and is also a very difficult concept to explore.  

I've worked really hard both in and out of therapy and have had success in managing quite a few of my BPD symptoms.  Exercising emotional control (not taking action based on emotion,) establishing a sense of self, and feeling more confident in myself.  I feel better both mentally and physically than I have in years.

All of the above falls apart when it comes to continuing my relationship with my FP. I still am able to go from the heights of ecstasy to the depths of despair because of how I perceive what they choose to do, think or say.   If I'm in regular contact and I feel connected, everything is right with my world.  I shower heaps of praise, gifts and adoration.   If I perceive them to be unhappy with me, or they make a choice I don't agree with, I literally fall apart.  I ruminate endlessly, I feel like I've been kicked in the stomach and I usually "split" on them.    I end up apologizing and the cycle starts up all over again.   This has gone on for years and it's exhausting.  I've tried everything (short of going no contact) to find a way to let this obsession go!   

Recently, I've come across the concept of projective identification.

"Projective identification is an unconscious phantasy in which aspects of the self or an internal object are split off and attributed to an external object.

The projected aspects may be felt by the projector to be either good or bad. Projective phantasies may or may not be accompanied by evocative behaviour unconsciously intended to induce the recipient of the projection to feel and act in accordance with the projective phantasy."  (http://www.melanie-klein-trust.org.uk/projective-identification)

It can be good or bad,  in my case, it's bad.   I feel like I've taken all of the emotions I don't like about myself and completely projected them INTO my FP.  My self loathing, selfishness, manipulative ways, haughtiness and narcissism.    

To make sure the "phantasy" works, I buy them over the top gifts (which they don't ask for) and adore them in a worshipful way.  This is unconsciously (until now) manufactured by me to make myself believe that they exhibit the behaviors towards me which make THEM narcissistic and make THEM act in a way which supports my self loathing.    Rarely do I ALLOW them to buy my dinner or if they show respect or love to me, I tend to dismiss it or devalue it.  Over the years, I think my FP has actually become who I "made" them to be.   They know they have me wrapped around their finger so they can do/say/act in any way, no matter how disrespectful or hurtful and I will always come back for more.   I'm not saying that I'm discounting their responsibility in all of this, but the truth is that this dynamic has almost completely been created by ME and my actions.

I have other relationships where the people have GONE OUT OF THEIR WAY to show me how much they care and love me.  I'm ambivalent about those people because they challenge me to look at myself and my less than desirable traits.

I LIKE to be the victim.  I LIKE to be the one taken advantage of and used because then I can point to the other person and HYPER-FOCUS on their  negative actions because then I don't have to focus on my own.

My mind was blown when I first was exposed to the idea of projection identification but it rings very TRUE to me and I think it could hold the key to freedom for many of us.     People often call their emotional connection to an FP as "imprinting." And in a way, if probably is.    But the imprinting part is really shifting all of those dark, yucky emotions into the other person.

What a realization to discover that my preoccupation with this person is NOT because of them or who they are but rather because I'm somehow injecting them with all the negative aspects of my own emotions that I, until now, did not have the strength to recognize and carry for myself.

I truly hope that this resonates with someone else out there or even maybe helps someone.   I don't know yet how this new knowledge will play out for me.  I do know that accepting this reality and looking at things as the TRULY are has already calmed down my feelings of anxiety and abandonment that I usually feel about my "FP."

I may finally be able to let go of the idea and concept of "favorite person" and instead interact with the people in my life as individuals with their own strengths and weaknesses.    Taking care of myself, loving myself becoming my own FP will one day make me the kind of person that doesn't need to project my darker sides into other people but rather take full responsibility for my own self and my actions.