Hello,
Divorcé of a nasty financial situation here who has helped others go through this.
He may seem reasonable now but it does change very quickly once they have someone new to impress and he wants to play Johnny big balls with her and sadly it happens a lot.
I know a woman who's husband got a £650 thousand pound pay out with work days before she found out that he was having an affair. In two years of messing her around with the finances, it was gone, he had a load of credit card debt and the only asset was their house which she then was told she would need to sell to give him his half!
Reasonable situations get nasty fast and often the wife calling out the changed or poor behaviour is painted as jealous. It's rough so while it is relatively calm get an overview of the financial picture and make an agreement and have it ratified by the court.
Financial splits work by adding up what each party has in assets and what each party has in debts and then working out how to split that number in two, you then negotiate how the assets are split. Debts accumulated during the marriage are part of this discussion.
You have a child to protect in this so however reasonable ex is claiming to be, you need this in writing and only discuss and agree financial agreements in writing. Even if it is a text after you talk to him saying "Hiya, just want to make sure that I understand correctly is this what we agreed today?" You don't want any situation where he could claim that you have agreed something different because once the money is gone, it costs tens of thousands to clear up.
Close the joint account. Debts that are his go into his name.
Take the child maintenance less the debt repayment which is an entirely reasonable plan. If he kicks off about it, you know that he was planning something to make his life easier that would have a negative impact on yours and your child's financial future.
I would strongly suggest using you free half an hour advice from a solicitor rather than asking Mumsnet.
I would look up the "form e" and try to fill your side in and get an idea of what his finances are like as this will inform the financial split between you and will help the solicitor with their advice.
I would also get a copy of bank statements, credit card statements, pensions, life insurance, bills etc etc so you have a view of the martial financial behaviour before the split as this will inform what your spousal and child maintenance should be. Also if you can download Martin Lewis' budget planner and fill in the costs for you and your child/ren for the year, that will help.
It is a lot of admin and in my experience it all falls to the wife and mother to prove what the child is entitled to but the more you do and the quicker you get it done, the less chance there is of him accumulating further debt or blowing through your savings.
When you have your meeting with the solicitor, explain your financial situation and see what she predicts the costs would be. Also ask what in their experience is a reasonable split of your finances.
Finally, I'm very sorry that you are going through this. Emotionally this is incredibly rough and being expected to do admin and cope with your loss and you child's loss is ridiculous but I do promise that once the finances are set in stone, it does generally get calmer. Good luck.