Much sympathy. I work in a much less stressful but therapeutic job and it is normal for me to spend the whole of Friday night 're-seeing' every patient I saw that day and questioning my decisions, waking at 4am a couple of other nights worrying about patients, to have difficulty switching off etc. I love my job and am quite happy but I can imagine what it is like if it gets more intense, more responsible, more senior.
My dh trained as a lawyer and worked full time for 20 years alongside a severe mental health diagnosis, he finally ran into the ground while working for himself! He'd left his job as he was in a terrible streak for years of having to be in bed for two days every fortnight plus doing almost nothing but work, eat and sleep because he was so ill. Even more stressful running his own business as nobody else to help manage the deadlines and responsibility, the anxiety overwhelmed him. After a bumpy few years and dreadful relapses including some triggered by ATOS benefits processes, things have been much calmer in the past year. I hope he might return to some volunteering in the future but am in no hurry tbh.
Financially, bear in mind that things change. E.g. when your eldest child leaves home, would you then be able to rent out a room and fund some university costs that way? Could they live at home for uni? Could they get part time jobs and contribute to the household? If you have garden space could you have some chickens and sell/eat eggs (not financially viable below a certain level though). It's worth also thinking about what costs you have due to work, e.g. transport, clothing, 'treats' to get you through the week etc. You could grow more food or get an allotment with more time.
Decide what life you would like to have (e.g. your partner clearly would still like to retire at ?65?) write it all down and make forecasts, then work out what the financial 'gap' is. Then think about how to fill the gap. By the way, don't waste your time thinking about wedding costs - the vast majority of couples expect to pay for their own weddings these days. That sounds very much like anxiety-based thought processes. Have you tried a mindfulness course/increased exercise? You'd have more time to do this without your job. I know mindfulness gets a mixed press in recent weeks but it has been a lifesaver for dh.