Oh dear god, I really don't know where to begin with this but I have to say something 
. For a start, you know he is not a good father, because relationship modelling aside (and that is a bloody good point) he is also controlling the children financially. Read back through your OP, look again at the part that says you have seen no rise in the money going into the joint account. He's been earning and accumulating more, hasn't he, so where is it? Your children have been growing, which means they will have needed more money for food, more money for clothes and shoes (and don't forget when they get to adult sizes you have to pay VAT on the clothes), let alone any payments for school trips or extra curricular activities. Your utility bills and your phone bills will have gone up, which means you've had less to spend on other stuff. Now, if he was genuinely poor it would be understandable, but he is not passing on the money to help you and the children.
He says he works hard, which is probably true, but who benefits? Look once more at your OP when you say you've not seen a rise in the joint account from the money he's been putting in. Do you want to know what the only question I have to ask my DH when I need some money from him? It's "can I borrow your card" and the only time he refuses is because he needs it physically for himself. That's because he - and other non abusive partners - realise that in a relationship financial control is abhorrent and that if I ask to borrow the cards it's so I can buy food, or nappies, or pay a bill.
You say he's being nice now? Really? So he speaks in a softer tone eh and maybe strokes your hair while he's insisting you can't afford this and you can't afford that. When he begrudgingly hands over some of the money. I can understand him wanting to keep some of it, but you are struggling whilst he is laughing all the way to the bank.
You say that he's clever, but really, I'd be prepared to bet that it's only because he uses long words (believe me I'm an expert at that 
) and doesn't let you get a word in edgeways that he wears you down. He's like those politicians you see being interviewed, who don't have a coherent argument but keep saying the same thing over and over without giving the other party time to respond. But you know he's wrong and abusive and reading through what you've put about him, both here and elsewhere, I can easily see he's abusive. As can many others. You are not imagining this.
So let's talk practicals now.
1: Any money you can save, set up a separate account and transfer the money into that. Actually, I presume he's over the threshold for you to have CB abolished soon and tax credits severely reduced or even cancelled. That raises an interesting perspective on those political changes, since it allows the greater financial control of those in your position. So let this be your incentive. Start making plans now. If he asks about the money (I'm presuming as a controller he demands to see statements), then get the money out in cash rather than doing a transfer. Say it's for food shopping, petrol costs, anything.
2: Get all documents together that you need.
3: Speak to the CAB or a free half hour consultation with a solicitor.
4: Keep this thread and read it when you are wavering. He will try every trick in the book with you, especially when he realises something is up (which is why he's being nice now). He will then claim he will take the children away from you. He can't do this. In fact, him ensuring you struggle financially to provide for your children will go against him.
5: You will not be doing anything rash. He can still see the children. But he does not have the right to control you in this way.