As for the comment about not paying the bills and mortgage....big assumption there! For everyone who doesn't (yours fairylea) there will be many that do
My experience - not just personal - but with the very many people I've come into contact with, is that this is exactly what happens. The XH promises the earth, only for that to be retracted shortly after. I don't know anyone who had all bills covered, mortgage covered, and child maintenance paid after a year. I know lots who were promised that.
Read the relationships and step parenting board. Almost everyone thinks minimum child maintenance is acceptable. For many people, it's seen as more than acceptable "DP pays the full amount to XW!" Give him a medal.
For many women, and the OP, it's wise to protect yourself as early as you can. I didn't want to get a lawyer, open my own bank account etc, because I didn't want to "rock the boat". But then it was too late. No access to cash or joint savings, no way to pay bills, my only income was £18 per week child benefit.
My XH isn't a bad guy. I like him. But the reality is that he earned the cash and I didn't. He paid minimum child maintenance on time every time. So I had to very quickly move from having access to £100k per year to £6k per year with almost the same amount of outgoings. Once I had a job, the £6k didn't even cover childcare costs. and I bet a lot of people think I was very lucky to get £6k per year in CM
It's bloody hard coping financially never mind the emotional ordeal of separation. It's good advice to the OP to protect her and her family's position.