@Givenupno
I sympathise with you on a personal level, purely because of the situation I’m in.
My ex and I have agreed a monthly sum (less than csa) but he also contributes towards school uniform, clothing and outside clubs. This wasn’t an easy reach but it works for us.
My new partner has a csa agreement with his ex. That was bitter so this is how I see your p.o.v.
One of his kids wants to live here however the ex won’t allow that. The child’s reason for this is because there is rarely food to eat at their mum’s, we hear what she spends her money on which in our opinion is misplaced.
That said, there are A LOT of parents who don’t contribute when they should (having seen friends in that situation) so I see where op (and others) come from.
A lot of men consider themselves the main income earner so therefore have the view (especially if the woman ends it) that they should keep ‘their’ money and the woman, left with the kids, should suffer - that is wrong!!!
Ultimately it comes down to your personal moral compass. My partner thinks all women are money grabbers whereas I’m very independent so he finds it difficult to understand why I’m not like his ex!