Chicory, congratulations on this important insight....
I really related because I had the exact same experience of being "saved" every summer by my greataunt who had this wonderful house on the beach in Connecticut. Those memories are so precious and indelible in my mind sometimes I get obsessive about wanting to "go home again." Unfortunately we can't do that. I have vowed, maybe as you have, to do what I can to recreate that serenity and normalcy in my own life.
But, as you have pointed out, what your grandmother did for you was not codependency--she was protecting a young, helpless victim--not enabling an alcoholic.
You are doing the right thing with your son, as painful as it is. He is making his own choices. He is NOT a helpless victim the way you were when you were young.
Recreate FOR YOURSELF the life your grandmother gave you--give yourself that serenity, normalcy, beauty and peace--and you will be honoring her legacy.