I'm really sorry you are dealing with this, at a point where he should be giving you all the love and support (emotional and practical) that he can, not behaving like an immature, cowardly douchebag.
I've said this to other people here, and will say it to you, too - protect yourself as much as you can by keeping records of any contact you will have with him. Keep texts, emails, letters, and if you talk to him on the phone or in person, note down the details as soon as you have privacy afterwards.
This is useful in all sorts of ways, possibly in any separation agreement, but also not least in stopping you feeling like you are going mad from all the mixed messages and changing stories you are likely to get from him. I still loved my husband even when I threw him out after he'd cheated on me, repeatedly, while neglecting our kids, and if I hadn't kept a record of our conversation I'd have gone mad from the gaslighting - him saying terrible stuff to me then denying it later, and changing his story every five minutes. It was a huge psychological help to me whenever he denied something for me to be able to point to exactly what he'd texted to me!
Good luck, Shocked. And focus, always, on what's good for you and the kids.