SMP

It is old school to think a man should provide, that’s pretty unrealistic as an expectation in today’s world. However it’s very off for him to turn around now and say he can’t afford to put in what he would have had to put in if you hadn’t made the extra money. Like if the idea was that you were on SMP then the plan must have been for him to contribute more for a few months? You’re the one losing earnings because of the baby he isn’t, he can’t just decide all your money is joint but all his is his. Idk sounds like you need a sit down open honest conversation about finances and the plan going forward. We pool everything equally and have exactly the same spending money each month. That way everything is fair and joint expenses are obvious and honest. If you know his wage and he really doesn’t have the money and is unable to make cutbacks rather than unwilling then unfortunately that does mean you need to look at ways to keep bringing in money and it’s not fair to resent him for that.

The important part of this story is whether he actually can or can't afford it.
If he can afford it then I don't think you should be having to pay every last penny leaving nothing for you.
If he truly can't afford it then I can see where he is coming from. If you're both struggling financially you may be entitled to extra benefits like UC so that's worth looking into.
I think it is a bit old school to expect a man to provide, not something I'd necessarily agree with BUT I do believe that in a relationship there is usually a breadwinner and they have a responsibility to provide a bigger share of funds - whether they are male or female.

It is old school to think a man should provide. However bills should be split fairly not 50,50. If he earns more and can afford to contribute the extra without having 0 leftover himself then he should. You both deserve to have money leftover. I have maternity allowance, and live at my parents house with my partner for a couple of months as were having a pain with houses but my partner does the bulk savings, we both buy our sons stuff when necessary, i buy any extra food etc things for us and we work other finances e.g. Christmas equally too.

I hate to say this but surely these are things you work out before living together.

Personally I think the total household income should be considered a total pot of money for the house, doesn’t need to be one bank account but total earnings are yours and his income added together. Bills are paid out of the total pot and then you both get a monthly allowance/budget to spend on what you want. What’s left over goes into savings/family days out/holidays etc.