How awful! Sorry you are dealing with this, but I have to give you some mommy props! Your post says nothing about getting back at dad or making him be better, you are just focusing on what you can do for your son without badmouthing dad, way to go mom.
I love the idea posted about going on 'dates'. Or just when you are out with your son, letting him know which things he does that are good and then encouraging him about things he doesn't already know. You are definitely the first line of defense here, so you will be the majority of the influence. And then find little examples all over- tv, movies, uncles, neighbors. Any positive male influence or example should be pointed out. This way, dad begins to be pale in comparison.
In psychology, the saying is this- from the same sex parent you learn WHO to be, from the opposite sex parent you learn HOW to be with others. Keeping that in mind may help guide you. Oh, I forgot to add library books, always good to find positivity in there! Good luck!