i agree that the dad who brought you up and loved you is your dad ,the difference is biological its as simple or as difficult as that.i had a tortured relationship with my dad ,he didn't want me, he wanted a girl,whatever i did was wrong etc....... i HATED him till i was around 39 years old ,i then made the discovery that my hatred wasn't really hatred it was the flip slip--sadness and longing ,this took me a long time to adjust to.i now see that he is a man with his problems he was an inadequate father and the way i healed myself was by beginning to love him in spite of his weaknesses,in turn i now have a good relationship with him.not saying this will work for everyone but it helped me.