Sounds like you don’t appreciate each other very much. Namely, the reason you have the luxury and privilege to not worry about money and do a low paid job you like is because he is working in high paid jobs that make him unhappy. Conversely, the reason he can take high paid jobs with long hours is because you are taking care of him and the children’s basic needs. I think you don’t say you appreciate him because he’s not saying that he appreciates you.
After 27 years it is easy for partners to start taking each other for granted. It then creates that feeling of just being a live in maid or a walking pay cheque depending on who’s point of view you are looking from.
I’d suggest that you start by recognising the good things he does for you and the family. Also point out the good things you do and that it would be nice if he could appreciate you in return.
Then tackle the argument with logic. He thinks you need more money, you think you have enough. So sit down and decide how much money do you need?
3 DC worth of university fees will be £45-50k each. Do you have £150k in the bank?
He earns a lot of money, but what do you have saved for your retirement years? How much is needed for you both to be financially secure?
Once you’ve jointly decided on how much money is needed, then look at his current income and your outgoings and calculate whether there is a shortfall or not.
Even if there is, would taking a job so far away actually help? Buying a flat and running it, paying council tax and utilities will cost a lot of money. Maybe the shortfall can be addressed by you taking a better paid job. Or maybe deciding to downsize and move to a smaller home when two of the DC have left for university. Brainstorm and listen. Don’t assume you have the right answer and argue about it. (Same goes for him).