I Feel for you OP. I understand completely because the same thing happened to me.
You will get through this.
You need time to process it, because it's such a body blow.
When you feel able to, go to your local CAB, they're brilliant. I remember sitting there with this lovely man who gave me so much practical advice about finances etc. He was very sympathetic and kind, talking me through it all. They will give you a list of local family solicitors, who will offer free initial session. See a few, find one you click with and get the ball rolling.
Go on entitledto.org, do the calculator as if you are separated, to find out about finances too.
Brace yourself for the discovery of OW. My ex denied and denied, but of course she was there. My solicitor asked me if there was one, and I told her he denied this. She said, "Of course there's an OW, they usually crawl out of the woodwork after a few weeks. Your husband will pretend they just met'. She was absolutely right. Lean on people, they will be amazing.
Don't think it's you. I wasted many weeks blaming myself.
You're playing catch up. He's way ahead of you, because you have been delivered a bombshell, but believe me he's been getting his plan together for months.
You'll be ok, the next few days will be incredibly tough, but you'll be ok. Too many of us on here have been where you are. We get it, we'll hold your hand. Reach out to your family, friends and us.
Take care.