What a dick. Of course there's no legal action he can take against you but still. What a shame your SS has such a jerk for a father.
I can relate because my step childrens father is a jerk and a con artist/used car salesman that would even scam his own son. While my oldest SS was putting himself through college working full time AND a full class schedule, his father pressured him into getting a credit card and maxing out the cash advance and loaning it to his father promising to pay back my SS, which never happened. He graduated last spring with a BS degree, a maxed out credit card and a ruined credit score.
My step children are older and thankfully we stay in touch and hopefully always will. We'll meet for lunch or dinner when we can. I hope that in the future you can stay in touch with your step son.