Hi OP just to reiterate that whilst your priority at the moment will obviously be getting through today (and I agree one way or another let his parents know how he has behaved), you are not in a hopeless position.
As you are married and have been for a long time, all assets are assets of the marriage to be split in divorce regardless of whose name they are in. That includes money in his bank accounts and the house. He has to pay maintenance for the children and depending on income may have to pay you maintenance too. Any divorce settlement will ensure that you and the DC are housed and provided for as far as there are assets available for this. He can't just cut you off (shitty though divorce is, you are a much better position than someone who is not married)
Look on www.entitledto.co.uk to work out what benefits you would be entitled to.
You may actually be better off once you have split.
Do not leave the house (unless you are afraid he will be violent) as otherwise you will be voluntarily homeless and the council will not have an obligation to house you. As you are married it is your house too. Does he own it or do you rent?
Go through all the paperwork and take copies of all bank statements, payslips, pensions and anything else to do with finances or assets. Put those copies and your and DC passports with a friend. Do this EVEN IF he purports to make up with you. Based on his performance it will not last and you need to protect yourself and your DC now.
Do you have a joint bank account? Take half out now and put it in an account in your name only before he empties it. You can open an account online and have the details all ready to transfer funds to on the 27th, which is the next banking day.
First thing in the New Year see a solicitor and (assuming he owns the house) ask them to lodge a matrimonial caution on the title to the house. This means he cannot sell it without dealing with your interest in it too. Ask your solicitor for advice on the best way to protect your position generally. If he has decent earnings go as fast as you can to decree nisi as that gives the court jurisdiction to order him to pay you maintenance.
In the meantime I'd suggest you do nothing to raise his suspicions that you are getting your ducks in a row. Just fade into the background as much as possible.
It is shit my love and he picked a particularly wanky time to do this, but you will get through it and come out on the other side into a better life. There are a number of us on the boards who have been through this.