Okay... I have so fallen into this trap.
Don't.
Take a step back and think to yourself
"More Proof that I made the right decision in leaving! Thanks! Because there is no way in hail I want to be with someone who would do this to anyone. Much less someone they're supposed to love! Bullet. Dodged."
And not fall for the trap of dignifying the argument / allow it to manipulate you back to "prove" anyone wrong. Anyone who would believe that about you you don't want in your life, anyway.
Those who matter don't mind
Those who mind don't matter
My ex is a sociopath (falling under the heading too, of "You'll never meet a sociopath you don't like"). I had to battle this guy in court. I'm x-military. I've never laid a hand on him. But dude fractures MY skull, and strangles ME... And I'm having to prove I'm the victim, here. Oh and about 72 other mudslinging nonsense. Like when Inhave my son I sleep until 3pm. 2 years of phone records, school records, work records to show that no. In fact. I do get up and take car of business typically starting between 4am & 6am. Hours and hours of work for each and every single one of his lies. Everyone lurrrrrrves my ex. This was a horrific battle, costing nearly 100k, and in the end he still got half custody (Oh. I think he really means that he wants to change). Vomit. I can't really blame the courts. I bought his shit for over a decade.
Seriously. Don't fall for this trick. Get out.