really feel for you, have been there too. The language he used etc is probably for the benefit of his new gf, once she gets over the initial dizzy feelings for him she will realise what he's like and think back to the way he treated you and not like him for it, believe me.
well done for getting out of the relationship, it takes some guts, especially when there is DS involved. Your son will be fine, he has you :)
This man isn't your problem any more, he is that other poor womans problem, history has a habit of repeating itself for people like that.
I would take a step back, if he is a good dad then he once you stop contacting him he will realise how much he misses his son and hopefully you can sort out some kind of mutual consenting contact. I agree about telling your son he's away for a while to let things cool off a bit. Do you mind me asking how old your son is?
I was where you are 9 years ago, I now am happily married to the most wonderful man with two more little ones. The ex, I know for a fact is still messing around behind his poor gf's back. But, her problem now, she set me free of him, she can keep him!
All the best, we're here if you need to talk :)