EX on Reddit doing smear campaigns

My ex cheated on me and it was traumatizing considering the therapist we went to knew and lied to me to, and blamed me and told me to look at my insecurities when I had doubts. Then when I discovered the truth they told me they knew all along and that I should be understanding

It was a lot going on in that relationship Including bringing a woman and children to his home whenever i wasn’t there, traveling with them, and more. Then pointing the finger at her

Now he’s on reddit doing a smear campaign about his ex wife (who he claimed cheated on him and lied about DV) I found out the woman he cheated on me with actually helped him get the case dropped

How do you all deal with this?

I want to expose him but my friends are tellling me know. But he’s the biggest narcissist and liar I know