OK op, you gather all financial information, out going, don't leave anything out, so mobile phone contracts car finance and insurance, keep a list of yours say fone and car finance,gym membership, and his separate, put together all house hold stuff including food, add that together, then days out, children's activities and nursery costs monthly, and holidays if any,
Your wage
His wage
You then have to agree % of who's goes into house hold, and family activities, again as your the lower earning you pay a lower % as you still have your outgoing fone, car, gym, insurance eg,
And remember if you decided to go full-time and need childcare or wrap around before or after school that's a cost that right now your doing at no cost, so if he wanted to be difficult it will cost so much to enable you to work full-time hours,
This isn't forever but for now until children older, and your missing out on building up your pension op,
When its all down on paper , you work out what's reasonable for you to pay , then put it to him , he carnt argue with black n white op, its there in front of him, might be good way to cut back on things too,
Things like, Netflix or prime, these things we pay out monthly without thinking whether we really need them ,
Good luck op,