He is financially ABUSING you. And I hardly ever use that word.
The question is, why are you letting him?
You need to add up ALL of the bills, including rent and utilities and demand he pays half. Perhaps you could put in a bit extra for food, as you have the boys.
He's also paying way too little child support, isn't he?
No grown man can exist on £70 a week. He knows it, you know it, and what's more, he knows you know, and that you do nothing to stop it.
FFS, stop being a DOORMAT.
List all the bills, divide by 2, and insist he pays that or fucks off.
Me and DH earn roughly the same. Our bills are about £2200 a month. He sends me £1100 a month. Job done. It's not rocket science.
HE IS FINANCIALLY ABUSING YOU AND YOUR CHILDREN.