Do not feel guilty. He should be providing for his children. It doesnt matter whos decision it was to split. I dare say you had a good reason. Could you ask him for a weekly/ monthly amount? If he says no then I would contact the CSA.
we feel out last week about money as he told me i should be being careful of money which pissed me off when he doesn't contribute. so bit worried about bringing it up but think trying to talk first might be the best thing.