Family Ties

What keeps certain families and certain members of families together?  I ask this because my sister has now come to the conclusion that she isn't really a part of my brother or my life.  I have known this for some time.  I have tried to rectify it on occasion.  I am nine years older than her and that makes a difficult situation that much harder.  She lived with her father isolated from me and my brother since she was about five or six.  So it has been fourteen to fifteen years since I have spent more than a week a year with my sister.  Most years I did not see her at all.  This is in no way her fault, as she was a child at the time. 

Now entering adulthood, it would seem that she could enter into my family as a presence, but we don't have that much in common.  Situations from our childhood we remember differently.  We did not have the years upon years of teasing and torturing that nurtures a brother/sister relationship.  It is almost like I never knew her.  Truth is, I don't.  How much of that five year old is left.  I have never known her friends and she was raised in a family different than the one I was. 

I don't have this problem with my brother.  We are only three years different and I lived with him most of my childhood.  We were split up when I was about fifteen.  We continued to see each other during summers and have made every effort to stay in contact with each other.  We have always shared friends, and, to this day, we get along with our each others friends very well.  Instead of growing apart while not together, we actually developed and became more like one another.  Independently we grew the same direction. 

I think my sister is jealous of this bond.  She feels left out and it hurts her feelings.  My brother and I grew up really fast and my sister still comes across as very immature to me.  Maybe as she grows older and becomes more responsible our connection will become tighter.  Maybe we will always be cordial to one another but never be close.  I still love her, but I don't know who it is that I love anymore.