Abandonment is something I would connect with a feeling of being vulnerable with someone. You find yourself in a vulnerable state with someone and then they leave you "high and dry" to deal with it on your own. Kind of like when a client has a strong transference reaction to their therapist and is sent away for it...without having properly dealt with it.

Rejection is more personal, I think. There's something about me that I want to give, but they don't want to receive. Very painful.