Like EaglesJuju, I also struggle with abandonment fears. When I was a child, they were physical (crying and calling my mom at 7AM to come pick me up from slumber parties, something which finally ended in middle school; crying when my friend's mom babysat me after pre-school/kindergarten on days when my mom couldn't pick me up). As I got older, they were more emotional. However, in my relationship with my pwBPD, they were both emotional and physical.
Change is something that triggers me greatly. When my fears are triggered, rational thinking and logic are eclipsed by extreme anxiety. When people have directly told me that they are not abandoning me, it made things worse at times. It made me feel needy, defective, and childlike.
When I brought up the fact that I was worried I wouldn't see my pwBPD that often after the school year ended (we taught at the same school, and she was living almost an hour away from me), she assured me that we would see each other. This actually made me feel worse and made me feel like saying, "But how do you know that for sure?"
My pwBPD is triggered more by engulfment than abandonment, so she saw my constant questioning of our friendship and of her feelings as being needy, and I can see why. That being said, she is the type who runs from her problems, so her past behaviors did nothing to assuage my fears. I knew she ran, and I was afraid she would run. Then, she would run. She would come back. I would once again be afraid that she would run. The cycle would repeat. I know my other friends won't do this, so I don't have these abandonment fears with them.
My pwBPD seems perfectly fine with not seeing any of her friends for long periods of time (months or years). She also has admitted to me that she reads every text that people send her but that she doesn't always reply. I am not fine with that. Not all texts require a reply, but some do, and it bothered me when I could see her posting on Facebook instead of replying to my texts. She does have some abandonment fears, such as when she visited her parents for almost two weeks in another state and hugged me like she might never see me again before she left for the airport or when I told her I couldn't hang out with her in my classroom because I needed to do work in mine and she told me she felt abandoned, but her engulfment fears overrule everything else.
Because her abandonment fears are not that bad, all I really needed to do was reply to her texts and let her know that I was there. I, on the other hand, need much more validation than that. Unfortunately, a pwBPD isn't really the right person to seek validation from.