AB
I would make an appointment to see the Business Manager at your bank and get them to do the donkey work for you and find out how you can resolve the business situation. Where there's a will there's a way! I'd also see the CAB, a Solicitor and Rights of Women which is a charity offering free legal advice to women so you know where you stand legally.
Alongside this, complete a claim for benefits online and your local job Centre will call you to arrange an appointment to see a Lone Parent Advisor who can tell you what, if anything, you might be entitled to claim; possibly Income Support/Job Seekers Allowance, Housing Benefit, Council Tax Benefit, Child Benefit, Child Tax Credits/Working Families Tax Credits etc etc. Also, is the bakery job part of your business or paid employment for another company? You can work out what child maintenance he would be required to pay at the Child Maintenance Options website.
If there is no way to salvage the business on the terms you want then you have to look at the bigger picture and decide if you can continue to live like this or not. One option, if you decide you can't, is to arrange an Individual Voluntary Arrangement, here is a link for more info:
www.gov.uk/options-for-paying-off-your-debts/individual-voluntary-arrangements
Obviously you want your children to stay with you, as you say, but you might be able to get some work that fits in with childcare options or it is worth turning things about on their head and thinking about retraining to do something else. Whilst the future is uncertain and as scary as this maybe it can also be a good time to make your life how you want it to be!
FWIW, I was in business with my XH, we separated and I gave him the business and kept the house, went to college and am now in my final year at Uni and can honestly say that it is the best decision I ever made.
if I can help at all with info or whatever then get in touch via PM.
Best of luck to you!