Advice on kid's father (my ex)

Ok, a little back story: I was with my kids father for 6 yrs and we had two kids who are now in elementary school. I was super young when we got together, and he moved very quickly to tell me he loved me and wanted babies and etc. I just got swept up in feeling so wanted, plus I was a very sheltered immature 19 yrs old. A few months into it, he showed tons of red flags that I ignored and he ended up being very abusive and controlling, on top of that nightmare he was a pill addict.

A list of awful things he did to me includes (but not limited to): threw things at me hard enough to leave huge dark bruises, poured drinks and things like salsa/ketchup/soup on me during arguments, called me a dirty whore and cornered and sprayed me with cleaning sprays until I was soaked, punched me on my arms and legs leaving huge deep bruises (he would say he "frogged" me therefore it wasn't punching and I was exaggerating, despite having really painful bruises), dragged me by my hair and pulled chunks of hair out of my head, and rolled up wet towels to whip me hard enough to leave welts on my skin. Arguments were usually caused by me questioning him about getting a job, cleaning the house since I was the one working, taking better care of the kids (I would come home and they were filthy and the house was obviously torn up from him not watching them), why he was texting a girl, etc. If I refused sex, he would keep turning the lights on and turn the heat all the way up in the house, pour water on me, take my pillows and blankets, and refused to let me sleep until I gave in and let him basically just use me to masturbate into.

Every time I tried to kick him out, he would climb in through windows or even just refuse to leave. If I tried to leave or call the cops, he would throw my car keys and phone so far it took me hours to find them. It was a nightmare. He blackmailed me, saying he would tell my family and friends terrible things about me if I left him, and that he would call cps and the cops on me. I was scared. Finally a neighbor called the cops and he was arrested and stayed in jail 3-4 months and I was able to get on with my life in that time and he pulled lots of stupid crap in the 5 years we've been split up.

I'm remarried and we have a good comfortable life and my husband now fully supports my kids and myself. My ex is close to $30,000 behind in child support. I'm waiting on a court date to take him to court, but you'd be surprised how hard it is to actually get these guys to pay. My ex cycles between disappearing for weeks or months, and then for a few weeks or months tries to clean up his act and see the kids and claim he loves the kids so much and is their father and wants to see them. I make him have visits at his mother's house supervised by his mother, because his mother has never disappeared on the kids and she keeps up visitation with them even when my ex is messing up.

Now, he has a new girlfriend that lives in another state. They went to high school together and rekindled on Facebook. She has 4 kids and is currently separated from their father. I'm not sure how long they've been talking but it hasn't been longer than 2 months. I keep tabs on my ex's Facebook because it gives me an idea of how he's doing and if I should trust him with a visit with the kids, and who he's hanging around or living with, if he's working, etc. Well, they've been gushing over each other saying they're in love and how amazing she thinks he is. How hardworking he is (which really makes me laugh, because he's never held down a job longer than 6 months and is unemployed more than working).

Anyway, my ex told the kids that he's getting married and that they plan on having a baby, he even told them the name they have picked out. Even though she still lives in another state (I have a feeling she's planning on moving back to be with him). I've been telling myself not to start any drama by telling this girl what a huge mistake she's making for herself and her FOUR children. Maybe he's matured, but I really don't believe people like him change permanently. And if she did have a 5th child by him, she'd basically be supporting her 5 kids by herself because even if he gets a legitimate job, the attorney general will take 60% of his paycheck until he's caught up. If he doesn't pay, eventually he will be in jail or they will have to hide him and then he wouldn't see my kids (which I wouldn't mind one bit to be honest). If she were to ever come to me and ask, I'd definitely tell her the truth but I feel like I'd just cause trouble for myself if I approached her about it. He's probably already told her I'm a crazy liar or something just in case I told her the truth.

Am I doing the right thing? And what the hell am I supposed to say to my kids, besides "well isn't that something". If you read this whole thing, you're amazing lol.

*UPDATE*

thanks for the responses ladies. I believe that staying out of it is the right thing to do, and that's what I'm going to do. I have moments of guilt for her children, and I would just hate if something serious happened and wonder if I could have warned her. But yall are right, it's not my business and MY kids are my business.

As for the comment about "stalking" his Facebook, I only check it when he messages me for a visit or when I'm trying to update his information with the attorney general, because I can usually tell if he's on drugs, or if he's working and where, from what is posted on there. I only happened to see all this new girlfriend stuff when he asked for a visit the other week. Believe me, I've wanted him to find a good girl to focus on instead of him bothering me but I didn't expect her to have 4 kids and want to bring a 5th into the situation, and that is what makes me question if not saying anything is the right thing to do.

I've decided I'll keep doing what I have been, trying to get the child support, making him have supervised visitation through his mother (who I do trust), and not approaching this girl about what I know. But if she does come to me to ask, I will definitely tell her the truth.