Always so much crap info given in these threads as 'fact'
That the marriage has broken down due to his affair has NOTHING to do with what happens with the finances.
I'm 15 years down the line from where you are. My idiot got the ow pregnant!
You won't feel like eating/sleeping but try. Soup, smoothies, cereal, toast whatever you can manage the shock will dissipate and your body will adjust.
Mon arrange appointments to interview family lawyers and find one you are
A comfortable with
B doesn't pull their punches.
If you have joint accounts open an account of your own with a completely different bank. Withdraw what is legally yours, arrange for wages, benefits etc to go into your new account.
Get onto the child maintenance department, tax credits, child benefit, dwp, council Monday if you need to change who it's payable to or may struggle financially and could be entitled to help.
Inform the school and any child carers so that they can monitor and support dd. Children often don't want to "upset mummy" but need a listening ear. Also so they are aware if there's any issues re pickup/drop off etc
DO NOT assume he will play fair they hardly ever do regardless of what promises they may make.
DO NOT go to his family for support. Ultimately HE is their family, not you. And whatever you say can later be used against you. Don't give them or him any potential ammunition.
If a family member can come and stay for a while to support take the offer - I had this thought I wouldn't need it - it was a god send!
Be as honest as is age appropriate with your dd. I defended, excused and lied for my ex in the "don't speak bad of the other parent" idea, it simply meant when she discovered the truth when older that she felt lied to betrayed and struggled to trust me on this subject. Since then I have been completely honest with her. Her dad and his now 2nd wife have tried to tell her all sorts of lies but I have offered and possess proof of otherwise so that they can't get away with that.
That said it is not her responsibility to referee the 2 of you. Nor to spy for either of you. Not saying you will or intend to but it happens. My niece and nephews had this shit from their dad, he also had an affair and yet was obsessed with my sister meeting someone else and pure interrogated his kids, they're now older and refuse to answer his questions.
Don't be tempted into revenge, retaliation etc it hurts you more than him. Don't give him the satisfaction of seeing how much he has hurt you.
Keep talking here and in real life to those who would support you.