For wanting my partner to pay more of the mortgage?

It was not a unilateral decision. They discussed it. From the OP's account he was not enthusiastic. Not being enthusiastic is not the same as outright opposition and saying he was totally opposed to her wishes.
To me it now seems as if he is punishing her by deliberately throwing luxury items into the shopping, claiming that as he now earns 90K 'his penny pinching days are over' and he can afford these expensive choices. But she is having to subsidise HIS choices. If he wants lobster, caviar and fillet steak, HE SHOULD PAY FOR THEM. He is a fucking hypocrite, needlessly pushing the food bill up and happy for her to 'penny-pinch'. I would have left an unsympathetic, selfish and solipsistic pig already. There is something unpleasantly punitive about his actions and him boasting about his wealth. I beg you, do not marry this c**t

Like normal people? What’s that supposed to mean?

We keep separate accounts so we keep our own autonomy. It’s important for us both to have absolute freedom. If I want to spend £500 on a chair, I can. If he wants to spend the same on a piece of tech, that’s fine.

Each to their own, it’s nothing about “normal”, it’s about fairness, respect and kindness.

So you took a financial decision that required him to subsidise you, which he wasn't very happy with, and you did it anyway?

I earn well.DH are happy together based on knowing we trust each other to contribute financially. We would support each other to take a slightly lower paid/lower stress role but thats not the same as dropping from 90 to 35k! It places a huge pressure on the other earner that wasn't expected.

I do not think you should marry this man. Or have kids with him.
You would be much better and happier opting for the single life.

You say you're getting married next year. Has he mentioned anything about a pre-nup ....?

He doesn't get to decide what you spend your money on. He doesn't get to tell you what type of food/holiday/luxuries you have to pay for.

Long-term, your options are

a) pool your money as a household, have equal say how it's spent

b) split essentials unequally (even though you presumably both use the house and the utilities pretty much equally) leaving you both the same spending money for luxuries

c) split essentials equally, and he has more money for luxuries

Why was he not supportive? This is his future life-partner.

I can never understand my money, your money notion. Maybe I am old fashioned but if you are a partnership and in love surely you do your best for your partner and work as a team. My DH earns more than me, but we just put our wages together and pay everything out of that pot. Money is the root of all evil as the saying goes. I guess because my parents always said that they would never argue about money I hold the same values.

She discussed with him. He wasn't supportive and she went ahead anyway. He never signed up to pick up her shortfall. She imposed that on him without his agreement.

I voted YABU because you made the choice to cut your income, and presumably your partner didn’t agree beforehand that he would pick up the slack/contribute more? Your partner was not happy about you changing jobs. Why could you not have just moved law firms, there are literally hundreds in London. You could even have come out of central London and not taken such a huge cut.

Now you need to cut your cloth - if that means you can’t go out as much etc then that’s the consequence of your choice. I would suggest that when you go shopping, you let your DP pay the bill.

To be honest, he's tight, Id worry about having kids with him.

My husband puts £1,500 in our joint and I put £500 because he earns more. He would never ask me to go 50/50 when he out earns me by about 40k!

Definitely try and iron out any issues before you get married - particularly how things will look financially if you have children.

You are earning a smaller salary so probably need to manage your own expectations regarding what you can afford lifestyle wise now. Less extravagant holiday/gifts for others etc. Your disposable income should be enough but if you’re still living the life of someone on your old salary, then it won’t be and I’m not sure why your fiancé should pick up the slack financially if I’m honest. If you were struggling, yes, but if you’re spending £900 a month and savings on rubbish? No.

Also, your mum is paying for your wedding! That’s another reason why I don’t think you’re as financially sound as you should be if I’m honest.

She did discuss it with him, so it is unfair to say that she made the decision 'unilaterally'.
This woman is his fiancée, the woman he has asked to share his life with him, his love, his companion, HIS WIFE. He should be delighted to be in the position to help her, support her and treat her to lovely things
He is niggardly, resentful, passive-aggressive and punitive. My partner and I have had fluctuating incomes over the 20 years together. I am now the higher earner, I am so happy that my income can allow us to have a good life-style for both of us. My partner is completely unmaterialistic, ( I am bloody well not!) money and possessions are meaningless to him, if he has a windfall he gives me the lion's share. I feel privileged to be able to pay for nice things, treat him, share wonderful experiences.
For those responding that she should refuse to go to expensive restaurants and luxury holidays and if he were to accept that and be perfectly happy to do these things without her, that is simply beyond my comprehension. If our positions were reversed and my higher earning fiancé happily indulged in his expensive lifestyle without me, I would walk out without a backward glance because he had shown me what his priorities were.

You aren't well matched. He wants to burn the candle at both ends while he can, whereas you went for a lower stress career before you even had kids.

Wow!!

He isn't affording it though, he's asking OP to subsidise half of it while he keeps the rest for himself. Just because he earns 90k doesn't mean they're joint expenses need to rocket to that level especially when it's on things only he wants to spend money on while she covers half of it.

Logically speaking, a proportional % of income doesn't work (in this situation) if it's being thrust upon one party

Once again theyre already paying a proportional % of their income except OP is paying the bigger portion and her partners got basically her salary pre contributions left over after his contributions. If OP had remained on 75k and not quite her job, are you still saying her partners salary should go up to 90k and a 50/50 split is still fair? If so you need to actually explain how it's fair for any reason other than "partner not happy!" You're accusing OP of living beyond her means while ignoring or not reading that her partner is adding his whims and fancies to the joint household bill - HE is loving beyond her and their means.

Again, they are essentially boyfriend and girlfriend. I'd have a very different view if they were married, and that would change, throwing children into the mix.

They own a property together and they're engaged! I agree it's not marriage but it still doesn't mean one can financially rinse the other (and no the one being rinsed isn't the one with leftover salary, accepting a loan from OPs mums, and getting a higher % of the house while splitting repayments 50/50 and.chucking expensive food and takeaways into the mix ).

This. @AnyPomegranate if you did move and then he advised he was stopping work to train as a self employed balloon artist, youd support him?

It's only fair if you can both trust each other not to take the piss though. Me and my ex did this, and when I got a promotion at work he went part time without telling me beforehand because "we" could now afford it.

Gross. I wouldn’t marry a man who would happily and peacefully watch me struggle to pay bills. I think by default men should pay the bills anyway, but I guess I’m just old fashioned like that ☺️

I think you need to stop wedding planning as you've got a huge issue here in terms of attitudes to finance and working together as a partnership. What's going to happen with finances once you marry? Have you worked that out?
This situation would be making me think about whether this person is the right one for me.

Great post.
Excellent idea to transfer your budget shopping money to him and he pays at the checkout. Much better than two trollies or two trips.

But that is just a short term solution. You still need to have the big conversation that I posted about above, to settle on your financial arrangements for marriage.

Because you CANNOT continue with 50/50 long term when you are supposed to be life-partners. For all the reasons people here have said.

I really don’t think you should go ahead with this wedding @AnyPomegranate
as it doesn’t sound like you’re compatible with this man.

YABU. You had an equal financial responsibility and unilaterally changed that, and now expect him to pick up the shortfall. I understand wanting to leave your previous job, but not leaving without working out how you were going to pay your way. On the flip side, you should be able to say no to expensive social activities if these are now beyond your budget.

Totally agree.

Get a second job.

You made a decision to reduce your income. It’s not up to your fiancé to subsidise your life.