Why do you let your Ex-loser-husband hurt you;ask him to be just cordial with hi and hellos;nothing else;you are divorced;
just talk about your son that to constructive talks;if he starts preaching,tell him :

'Mr EX-Husband!!!I am having deep problem now;I struggle ,not to drink and heal myself,I am helping myself to get to talk to therapists,but money is short,I am not able to be with my son whom I love deeply;IN SHORT I am suffering deeply now ,AND YOU RAN AWAY,you are a loser,a fake person ,not a real one;But do not worry ,I will COME OUT OF ALL THIS MESS STRONGLY ON MY OWN,AND MY SON WILL LOVE ME FOR THAT';AND STOP PREACHING ME;If it was in my HANDS the SON would be with ME and NOT with YOU;Henceforth ,if you want to talk,tell me things WHICH will be conducive to my well-being and not to demoralize me;I know I am very good human and need no crappy talk"""""""

I guess this will keep his mouth shut ,What say Melstar!!!!!,and if he is human enough(irrespectve of the fact that the loser chose to run and divorce),yet he will help you positively in dealing with your son;