I'm terribly sorry you're going through this now.
It's easy to say but don't blame yourself if you decide to try and park making big decisions until you're recovered enough to look after your DCs safely. You can then, if you choose, end things. I doubt your husband (and his girlfriend) have a heart. For what it's worth, if he is able to treat you this badly, she should already be able to see what he is really like.
It might feel unbearable now and I realise it feels like the worst time to find out. In years to come, it might have been better to find out about his vile nature while you are younger rather than coming out of decades of an unhappy marriage with perhaps no career or earning potential and fewer choices. That said, I would think what he has and is doing is close to unforgiveable.
Sorry if I've said anything wrong, his behaviour is terrible and I'm trying to say something helpful though I realise there probably won't be a right thing to say.
As PPs have said, do you have any family who can come round to help, offer support and look after your DCs (who I expect will be worried about their DM).
I hope the treatment and your recovery goes as well as it can and you get back on your feet and able to kick him into touch as soon as possible.