Plain and simple quacking. Offense is the best defense for an alcoholic. He's playing mind games to tear you down and so he can be right. Don't get sucked into this. You didn't cause any of it and there's no use in arguing with a drunk or a dry drunk. How to respond? Don't. Block his calls and messages and get back to enjoying your life again.
I have a hard enough time trying to enjoy tiny rare bits of time with my husband who's 80 days sober. He's still trying to get his footing in a world he's not used to and each week it seems his brain is leveling out a little bit more -- very slowly. There are still moments where I wish I could have a few months on my own and not have to deal with the alkie-brain thinking anymore. I wouldn't recommend trying to stay friends with a former boyfriend who's still drinking and denying there's a problem. No matter what you do, put your son and yourself first and figure out what's best for you. If your X ever chooses recovery, then perhaps a couple years into that you might think about keeping in touch. Chances are you'll both be completely different people in a couple years, whether he's drinking or not. Keep working your own recovery one day at a time. Even though the relationship is over, you can still go to Alanon or Celebrate Recovery.
Congrats on the progress you've been making and the happiness you're learning to find. I hope you're able to put things in perspective soon. (((hugs)))