I'm so sorry OP, you're well rid of him 
The OW sounds like a spiteful woman, just remember her karma is the cheating git she's shacked up with and she will reap what she has sewn.
If he can betray his wife and mother of his 5 children then she's got bob hope of him being faithful to her, at the moment she feels like she's won some sort of prize but what she's really done is taken a useless deadbeat dad off your hands. That man is not a prize.
In a year or so from now you will be in a different place, healing and getting on with your life without him and the likelihood is she will soon be where you are at. I think you could be forgiven for feeling a bit smug about it when she is.
Retake control of your life and laugh at them, when you're able to.
Men like this should get themselves sterilized and stop mass producing children they then wash their hands of. How dare he imply that you shouldn't have had all of his children.
In your darker moments look at your children and remember they need you, they're not at a loss by not having that man around but they'd lose everything if they lost you. You are their entire world.
I probably sound very bitter in my post and that's because I have gone through something very similar, so i can tell you that things will get better I can promise you that.
He may try to test the waters with you in the future when things go tits up with OW (which they will) and when that happens you need to stay strong and remember he has shown you and the DC exactly who he is.
Sending you strength