Your dad leaving at such a young age could have subconsciously affected the way you perceive relationships. The struggle you faced / face to reestablish this relationship could have caused you to be reluctant in allowing people into your life because you fear that they too will leave you.

In order to protect oneself from the potential or perceived distress of a failed relationship, those with BPD have a tendency to “push away” from friends and/or loved ones.

BPD is difficult to diagnose, and a lot of people have misconceptions about what it truly is. There is much more to it than problems forming/keeping relationships, so perhaps read a little further into it and see if it sounds familiar. Obviously, you know yourself better than anyone.