I have some experience that relates here:
I grew up without a father since he was in prison for 15 years of my life. However, I had two grandfathers. My Grandfather by genetics was an abusive alcholic. He beat my grandmother, shot a gun at her once, he held a knife to my uncle's throat once. Since my mother was 16 when she had me, I remember some of this.
Fortunately, my Grandmother managed to divorce him and found another man. He was a great guy, ideal father and grandfather. He treated me, my grandmother, my mother and uncles like gold. Unfortunately he had poor health and when I was a kid I often had to stay with him in the summers to watch over him incase he got more ill while Grandma went to work. Those days I spent with him were by far the biggest influence on me as a man. I learned what being a man was from him since he was really the only male role model I had. So of course, when he died when I was 9 utterly crushed. To be honest, at teh age of 33 today, I still miss Grandpa Joe.
He was the one who took me as his own when he had no obiligation to do so while my biological grandfather was an evil man and my father no better. So, Grandpa Joe was my GRAND FATHER (two words, father and grandfather all in one). We shared not a drop of common genetics, but that's not what makes one family.