"I'm not a fantastic parent.
I'm poor, depressed and stressed out of my head.
I have zero family support - no parents, nothing."
not fantastic because you've been subjected to severe abuse at the hands of your husband. Without that happening, you will find yourself again and rebuild your life.
Poor? and? that's what benefits are for - tight, but doable. Child Tax Credits help with childcare for after school etc.
Stressed? no shit! ANYone would be, living like you are... breaking free will reduce that immediately; the effects would be felt not long after.
Depressed? see above
zero family support? same as lots of people; get to know your community - Children's Centre, homestart, gingerbread (for single parents), preschool groups; find a hobby and get some adult time to make friends again... it'll happen. I'd recommend the Children's centre as the first port of call, though.
DO NOT believe A WORD that man says. If you left (with the children), you would be supported by every single agency available to you, including Social Services if they received a referral and assessed the children as needing support. Nothing you have said here indicates they'd look down upon you unless you refused to work with them... (IF you were on their books, so to speak - no guarantee that'd happen either)
Regarding him being a "good dad" - he isn't. He is subjecting his children to severe emotional abuse and neglect. That is NOT looked upon well by any agency.
I promise you - he is NOT a good dad, regardless of whether he leaves the children with his parents, buys them all the gifts they want and can afford a car and holidays. Those things do not make life safe for children.
Stability, calm, love, care do .... you can not leave the children with him - he WILL continue to abuse them too. You've been fed a bag of lies for the last x years this behaviour has been going on - and before; grooming you to take the abuse as he ramped it up slowly, invisibly. You can not trust a word the man says - especially when it's about your rights, your responsibilities and your role as mother.
Call the DV 24 hour line - 0808 2000 247 when you're safe and alone to talk to someone about it all.