Op I'm sure it has been a shock especially his reaction.
I'm coming at this from the perspective of having been married to a spender where I'm a saver but naively we thought all married couples had joint current accounts and just pooled all their money - that's how both sets of parents did things and both our mums had been sahm at points because in the the 60's and 70's there simply wasn't much in the way of childcare.
It wasn't until much later we learned that they too had bumps along the way due to one being a spender and the other a saver.
They had sorted things out their own ways and we took advice from both and used the elements that worked for us but weirdly what we never considered was separate accounts.
We earned roughly the same but ex was used to having more of his money being his own to do as he liked because until we married (we didn't live together first) he had low outgoings due to being in the army. And they were almost all deducted at source so he didn't have to think about it.
His rent was very low (but it was really just essentially for a room in barracks - shared bathroom and small kitchen), mess fees heavily subsidised for excellent food, minimal amount for a fee that was akin to council tax (they don't actually pay council tax in barracks then not sure about now, but there was another thing I forget name now which covered that), his uniform was free of course and much of his kit. So all he had to pay for out of what was left - which was a good amount for a young single bloke then - was for nights out, his sports hobby (again through army so largely subsidised) transport if needed and "civvy" clothes/shoes if needed (which as he mostly lived in uniform and if he wasn't going out of an evening he'd just kick about his room in joggers/tee wasn't often)
So when we married and he suddenly had real bills to pay it was a bit of a shock to him, he'd never had to budget before!
After our first few months together it was stressing me out that he'd regularly dip into the overdraft without batting an eye - his attitude was he was in a very secure job and would definitely be paid next month so it was no problem. He also didn't know that being overdrawn cost! No idea why he thought that.
There was one almighty argument as a result of his actions leading to me being embarrassed in the corner shop when card was decline when I thought there was over £100 in the account.
Once we both calmed down we sat and went through all our bank statements (I'm very organised type and had them all in a folder paper statements then) and then income and outgoings and eventually agreed a personal spending amount.
At first he tried to argue I spent as much as him on my personal stuff but we went through the statements with highlighter pens and added up who spent what and his personal spends well exceeded mine! He was shocked how much he was spending (at the start of the discussion he'd said a rough amount what he thought he spent - it was 1/4 of what he actually spent!) he was also shocked to learn that overdrafts cost money - inc fees for bloody letters from the bank he was almost apoplectic at that and nearly complained to bank, I had to explain to him he'd agreed to that when taking out the account and that actually I had told him this when we discussed arranging the overdraft as a buffer he'd forgotten.
So from that point all well and good, we set a budget together, reviewed it annually or when there were major changes to income or outgoings or planning a large purchase.
When planning dd we saved for my mat leave (wasn't as good maternity pay in law then as it is now) and again set a budget.
Fine until we split. I was a sahm at the time having previously been a childminder (I had suspicions of affair and I had charges that were moving on and as we were in army accommodation I didn't want to take on new clients that I was worried I'd soon be letting down), that came to a head and we split.
He'd always been very vocal about how men behaved following a split (but then he'd always been vocal about cheats too) so I was shocked when 2 days after we split, knowing I'd no other income he completely wiped out the bank account, took the family car without a word to me and some valuables from the house again without warning.
It was a horrendous situation. I was far from home, no support network, no job, about to be turned out of my home with no right to claim council housing where I was as I had no familial or employment connection to the area.
I had to borrow money from a neighbour I barely knew at that point (we became good friends) and then repay them when my parents were able to pay in money to the bank and I was able to get to a branch to lift it.
Never been so low in terms of financial security in my life.
To give you a sense of how "out of character" my ex's actions were for him his own family and close friends since childhood genuinely believed he was having a breakdown. He wasn't but he has changed a hell of a lot.
I now advise others in real life and on here to just protect yourself financially as much as you can.
People don't always realise how vulnerable they are.
I've said on here many times also about the relative I saw being left seriously stuck when her partner died intestate. She was also a sahm to 2 young dc. The house was in his name because she had no earnings to go on the mortgage/deeds, because he was young fit and healthy it didn't occur to them to have his life insured and as I say no will. As a result she had to leave the family home and go back to work full time while she and the children were still very much grieving. She had got along well enough with her "in laws" before he died but after they claimed their legal rights to the family home etc.
It's frightening what you read on here sometimes what people believe they would get legally in the event of a split, or spouse/partner becoming incapacitated or dying.
Marriage provides some protection and I'm glad I was married to my ex as it gave me some recourse on some matters but in hindsight I would have been better off
Having my banking completely separate to his
Working outside the home full time and having dd settled in childcare
Having some savings set aside (we did have savings but again joint account which he emptied)
Having a credit card just in case (I didn't trust them at that point but now know better. Pps are right they have their uses if handled sensibly)
Had my own car even if it were just an old "banger" rather than us having 1 much newer car between us.
Hindsight is 20/20 you are where you are but hopefully you can sort things so you're less vulnerable.