OP, this isn’t a sudden decision on your H’s part.
The fact he’s taken your passports indicates he’s been planning this for a while.
You need to go into self preservation mode.
Get an std check, he’s screwing a random off the internet, I’d not bleed ever this was the only time.
Open a bank account in your sole name and empty funds from joint account into it. I am willing to be you’re going to get a shock when you check joint accounts.
Have your salary sent to your personal account which he has no access to, do the same with any benefits you may receive eg child benefit/tax credits.
Rally around friends and relatives, tell them what happened.
Get yourself a solicitor.
Get financial advice, start with citizens advice to check what you are entitled to.
In your position I would set up a child maintenance claim too, it takes months for them to collect the money I’d do it now.
Apply for new passports ASAP.
Move all important documents somewhere safe. Eg birth certificates etc.
You need to be practical and level headed right now. Sort out your finances quickly.