Elegance
What a complete shit. So sorry that you and your sons are being treated like this.
Yes, you MUST get legal representation and now. Another thing to if the house is in jopint names it to apply for an exclusive residency order so that you and the boys can stay.
You need to start making a log of his contact with you too.
Keep any e-mails, texts and try to write down what he says to you, and visits to the house etc.
DO NOT MOVE OUT OF THE HOUSE.
You sound like you have some great RL support from BOF, but you need to get some legal help too.
He is having an affair, not you. He is being unreasonable, not you. He has left the marital home, not you. He has done this, NOT YOU.
Re the money he 'doesn't have, well, that's a touch one to prove if it's cash rather than in the bank.
Do you have a joint account together? If so, go and get as much out as you can.
Stand your ground. And keep posting. Let us know how you get on.......