Is this Grandfather, the dad of your Mother?
I have relatives on my dad's side of the family, my dad having also died of alcoholism that now give me the cold shoulder, when I was drinking we were the best of friends, we would share many drinks together, life was great, lets all get hammered!!
But when I got Sober it started to raise questions and a sadness within them, I had gotten Sober, rebelled against the natural order of things, my dad so to speak drank himself to death, and every time they now see me they are reminded of the choice that my dad failed to make, he let alcohol take himself to the grave!!
Not saying this is the same, but your grandfather looks at you, you are the success, the Sober person his daughter couldn't be!!
Out of sight out of mind if you like, I'm only speculating, but hurt and resentment of alcohol can arise in many different forms, it was something I really needed to come to terms with when it came to my dad's side of the family!!