My dead beat ass baby daddy

So I had my second baby boy. My kids dad and I are on good terms well atleast I thought we were. My kids and I go to visit my mom in another state and while I'm out there I get a message from this girl asking who I am so I told her. Come to find out this Bastard has been in a relationship with her for 4 months. I'm devastated. He has been lying to me about not having money when he was being Mr flashy for that bitch. Then he had the nerve to deny our kids. Y'all at that point I started to see RED. I lost it. I came back home and filled my child support papers. This Nigga since we been broken up has only seen his kids 3 times. No calls nothing. So now I'm going to file for full custody. And now he's trying to turn everything on me.