heartbroken - it's all part of the script.
He may be feeling some level of guilt about his leaving/cheating; but he won't like to feel guilty, so he will turn it all around so that YOU are the guilty party, the reason he left. YOU did it all wrong, you made him feel like he had to escape, YOU are the "bad" one, not him. So he keeps up the barrage of abuse because it's him making sure that he keeps his own guilt out of the picture.
I know it doesn't make sense to you, why would it? and that it's incredibly hurtful, but now he has "checked out" of your relationship, he has changed, pretty much irrevocably. All the character traits of his that didn't "fit" into your relationship, that he may have suppressed over the years to try and fit better with you, all of those will be coming to the fore now - this is why it's quite common for people to say "he's changed completely" or "I never knew he was like this" after a split.
He is re-writing his history with you to justify leaving you - you are already someone you wouldn't recognise if you heard what he said about you.
Please get off his social media. Block him. Have one email address that he can contact him on, but stay away from his social media, all you would be doing is poking the wound harder. You won't hear/read anything good on there.
And as others have said, don't rise to it. Stay calm and icily civil - this man is not the man you loved and were married to, he's someone else now.
So very sorry to hear you're going through this, it is utter shit and can take a long time to get past - but you will. One day at a time, stop and breathe - you can do it. 
