Melanie, I know you want an answer as quickly as possible. But this is your life and I want to make sure that the answer I give you is the most fitting to your specific situation and who you are. So I need to ask just a little more:
So, this is a new experience in your life. In previous relationships you did not find yourself pushing the person away only to want him as he moves away. You then hint that there's quite a story about this relationship involving a lot of indecision on your part. Right?
It's therefore no longer clear what this might be about and I don't want to give you just a generic answer. Is this wanting him part of a whole situation that's specific to your relationship with this man?
As for the questions about your childhood, they were aimed at understanding how this desire as he leaves situation might fit into your life. But that seems questionable now (refer to above).
In general, though, the question of how our adult lives are influenced by our growing up and child lives is the subject of a whole lot of psychological literature. And therapy. In fact, I'm working now in therapy with a person via Skype about her sense of self and her sense of ambivalence in relationships based on her growing up with a father and stepmother much as you describe.
I'll await your reply and respond when I log back on.