With my wife, including Mat leave when she earned a lot less, we had a joint account that we both paid into, such that we kept the same amount back each month for ourselves.
Joint account covered all expenses - mortgage, bills, childcare, food, putting savings aside for kids, holidays, car payments, saving for big things like new kitchen. So one job of course is working out how much per month that could/should be.
Fake numbers:
So if joint accounted needed £2k a month, I might pay in say 1500 of my 2k pcm salary, and shed pay 500 of her 1k pcm. So we're both left with £500 each to do as we please, including whether to save any of that, or bolster pension etc.
Of course, under this arrangement, if I'd say earned as much as £3kpcm then I'd have paid ALL joint expenses (I'd pay in 2k and keep 1k, she'd have kept all 1k of hers). Maybe some would frown at that but I wouldn't have.
Of course what we then DID 'debate' was which car to get, or whether to include a wine fridge in the new kitchen etc (with me being the more frugal) which affected how much the joint account needed. But that's a separate issue!
Ask him why he'd see that arrangement as unfair! You're a team, not adversaries (from a man)