Have you had a good heart-to-heart discussion with him about how your joint finances as a couple will work after you are married?
There are three main options:
First: Everything pooled. All income from any source you goes into a joint current account (and a joint savings account). i.e. your salaries are paid straight into the joint account. You then decide together how to spend.
This only works if you have broadly similar tastes and values, so you are naturally in agreement about what standard of living you have as a couple. It won't work if one person is a saver and the other a natural spender.
It also means neither person has any financial independence, so it is terrible in cases of domestic abuse.
Second: Proportional split. You both pay into a joint account according to your income, and have separate accounts for 'personal' money.
This sounds fair in theory, but in practice if one partner earns a lot more, they get a lot more personal money. So a person on £100k paying 80% into the joint gets £20k for themselves, but their partner on £30k paying 80% gets £6k for themselves. This can be a recipe for resentment, unless the higher earner is generous by nature and happy to pay for shared holidays, treats for both people, etc. out of their personal money.
Third: Equal personal spends. Everything is paid into a joint account, like in option one, but then each person gets the same amount transferred to their personal account, e.g. £500 per month or whatever you budget, for 'pocket money'. This means you both have the same to spend on luxuries and treats without feeling guilty that it is coming out of joint funds.
If you both earn a lot, there is the option to have a higher amount transferred for 'personal' money, and you each keep your own savings, or you keep the personal money low and have joint savings.
Joint costs are all household costs, and all costs to do with children. Phones, cars and pets can be negotiated as joint or personal. Treats like meals out can be joint if you both agree and can afford it.
Mortgages are joint, even if one person earns a lot less, because after a long marriage the house is a joint marital asset in the event of divorce, no matter who paid what. Although if one person put in a much higher deposit that can be ring-fenced legally.
What is NOT an option is continuing with 50/50 on all costs. It doesn't work over the long term as incomes fluctuate, and is most definitely not fair on a woman who has to fund maternity leave and years off work or in part-time roles to cover childcare.
What if one of you became disabled and couldn't work again? How could they pay their 50%. What if one of you got made redundant?
50/50 is for flatmates, not life-partners.
You need to have this conversation with him before continuing with any more wedding plans.