I could have written your post OP.
DH and I have been together since we were 19. We're both now 46.
He has had anxiety and depression his whole life.
He had a stable and loving home life, horrific bullying at school.
It has affected everything since.
In our early twenties I was genuinely worried that he would have to be sectioned under the mental act. He didn't cope with much despite doing fine in life, setting up his own business etc. All he could see was how much better everyone else we knew was doing (financially, which was what he obsessed about).
He eventually went to the GP who put him on the waiting list to see a psychologist. He waited 3 years. This exacerbated his depression and anger. He developed a physical tic from the anxiety.
He got his 6 NHS sessions with the psychologist and did start to make a little progress. The psychologist referred him back to the GP for anti depressants. He took them for several years. Things definitely improved. We had 3 DC. If he forgot to arrange his prescription in time and there was gap, I definitely knew about it, he was awful.
The GP was keen to meet targets and get DH off anti depressants so basically made him go in and beg for them.
DH decided to wean himself off ADs and find a counsellor and pay for it himself. He has spent many, many years with this counsellor now and worked very hard at changing things. I applaud him for this, it hasn't been easy. However, he spent many years trying to progress but simply was not coping.
Out marriage was absolutely intolerable. Many things said in your op were exactly my experience. It took me a very long time to come to the conclusion that I was going to have to leave with the DC and I started to make an exit plan.
Our communication was non-existant. He seemed unable to see my point of view as he was so mired in his own anxiety/depression/mental pain. I closed down as a mental self defence mechanism and tried to get on with protecting the DC and just trying to get through the days.
We made a bit of a breakthrough in communication. DH somehow got the feeling that I was planning to leave (things were very bad at that time). I had done a lot of reading over the years around DH's mental health problems and had thought he needed to go back on ADs if only for the short term to try and level out a bit.
He agreed to go back to the GP who was very supportive at this time and issued a prescription for ADs.
Before DH filled said prescription he went to his counsellor and talked it through. The counsellor was not a fan of ADs and thought that the problems would all still be there and not resolved, that he just had to keep on working on them.
DH threw the prescription away. He continued counselling. Nothing improved. We limped on, I'd lost the momentum to leave in the hope that we could change things. I fucking cursed the counsellor. She didn't have to live with him. I did.
Somewhere in the meantime DH had read an article online about SSRIs being a load of bollocks and the the placebo effect.
I had read differently but what did I know? I'm not a mental health professional. He wouldn't take it from me.
DH eventually stumbled upon an article about persistent depressive disorder (dysthymia). It basically described his whole life. It means that he needs ADs permanently. His brain chemistry doesn't work without them.
I already knew this.
He went back to the GP who had never heard of it but was open to listening and agreed to give ADs another try.
He went to his counsellor who had also never heard of it.
He still works with her on a regular basis. I have no idea how much he has spent over the many years.
The result though is that he is unrecognisable now from the angry depressed arsehole he was at one time.
He is very loving, patient, attentive, tolerant, a great dad. A different person.
This is not only the ADs, he has worked hard on this and does every day.
It has taken a long time to settle into this new way of life. For a long time I was waiting for the regression and to have to prepare for flight again.
We are now happier than we've ever been.
OP, I don't know what to advise really. This is just how it turned out for me. If I had ever posted any of this on MN before then it would have been a resounding LTB from every responder (I've been on MN for more than 15 years now, I know well enough how this is viewed). Perhaps if I'd had the courage and got my shit together sooner I'd have gone.
If your DH is willing to get the appropriate help and support, perhaps there is a way through.
I wish you all the best OP.