Jeeze Stig, oh dear, a bit of a mess. There has been some very good advice on previous posts so I'll try and not go over old ground.
YOU have made the hardest first step by "talking" about what's bothering you, albeit through a forum with (probably) strangers.
I empathise with you.
During the pandemic I developed anxiety - my wife was/is on the shielding list and I work in a smallish building where we have approx 200 people from all over the country on a regular rotation that I was in close proximity to. After struggling for several months with only getting 3-4 hrs sleep a night I finally went to see a GP - He diagnosed anxiety, have been on medication since which helps me sleep through the night (mostly). My ability to deal with stress nowadays has been severly diminished.
During this time my employer was trying to push me to do a job I wasn't employed to do; it caused me so much stress I ended up in tears at work, sobbing like a child. To this day I still feel a mix of shame and embarrassment that a 50 something bloke acted like this, but I also know that it wasn't "me" and that my mental state was out of my control. I didn't go to see a GP, we're men after all. With hindsight I now know I'd had a nervous breakdown and wish I sought help then.
A couple of months ago I had my second work related nervous breakdown in 2 years - again related to proposed changes at work. With hindsight I should have realised I needed help before it happened - for maybe 6 months prior to this my colleagues saw happy smiley Neil at work but inside I felt sick, "lost" and that I could burst into tears at any moment. One day, nothing in particular happened but I couldn't stop the "emotions" welling up and just walked out. Came back an hour later and had to explain, choking back tears, what was up. My supervisor was sympathetic and told me I had to go to the doctors there and then, If I didn't they would take me. I'm glad I did. My medication was increased and I feel more settled in myself, today I had my first meeting with a therapist from the Charity MIND. Another session next week - will it help? Who knows, but it's not going to make things worse anyway!
What has all that got to do with your situation? Maybe buggerall but please, please go and chat to your GP. Don't let yourself get to breaking point. It's harder to bounce back. Mental health doesn't have the same stigma it once did and I feel no shame/embarrassment telling people I have mental health issues. Heck, I've just bared my soul to you lot!
I think someone else said similar but don't get friends involved, get professional help. It's usually easier talking to a stranger than someone you know anyway and they'll be objective.
You and your partner are a team. As someone else said "we need to get help for the hoarding to help our relationship" is supportive rather than "you need to get help...."
You mention your ex-services - my manager informed me that there is a Civil Service mental health charity that has a helpline open 24/7 365 days a year. I don't know if its available to ex-services but if you are interested drop me a PM and I'll get the phone number for you.
Aside from my problems(!) here's a few thoughts for work...
I've had a number of occasions over the years where I've had to be stubborn/ dig my heals in/ be awkward to my employer ....
In a previous role I had to inspect the forklifts at the start of each day. I like to do my job properly and often had to take the keys away as, for example, the amber beacon or horn wasn't working. They didn't like it - "how are we going to get pallets of of the warehouse? Work will stop!" "Not my problem" was the reply. Within days an engineer would be on site repairing it.
More recently my work supplied safety boots were falling apart but HQ were dragging their heels over replacing them. After 3 months of waiting I sent an email notifying them that I was no longer prepared to wear them and that should I suffer a foot injury they would be liable for any compensation, this email is a record that I have notified you. Within 2 weeks I had a new pair of boots.
What I'm trying to get at is put it in writing in an email your health and safety concerns, you then have a record.
If your the site manager and I presume have some sort of health and safety duties, tell then they have XX days to rectify the faults with the building or you will board up the door for everyone's safety. If it's raining and water comes through the electrics refuse to enter the building... Sometimes one has to let a process fail before anyone will do anything about it.
Make sure you have a record... if they sacked you you'd have evidence for a tribunal....
On a happier side note if you needed a cheap weekend away in Wales drop me a PM, we have a small wood/ Ash plantation you could put a small tent/ hammock up in (or dig a harbour, lol), campfire, picnic by the stream... Pen y Fan 10 mins away... Reminisce the glory days on SENTA...! I'd have to run it past the wife but she's not SWMBO, we're equal! Might even let you take a log or two away for turning!
You've taken the hardest step in opening up, the second and third get a little bit easier...
All the best
Neil