The toddler analogy certainly illustrates the arrested emotional development of pwBPD. It's interesting to consider how a simple, F.Y.I. gesture (like forwarding an email) can satisfy them emotionally and yet be so emotionally challenging for us.
The fact I initiated contact by forwarding our colleague's email to him was proof that I have not forgotten him and still care. Now he is ok again, and can go on doing whatever he is doing, until he needs to run back to me for a shot of reassurance.