Okay. Firstly, there is a difference between "having a mental illness" and "being an arse". You can be both at the same time. While you are not responsible for things that are a result of your illness, you are totally responsible for being an arse. Your husband sounds as if he is depressed, but he also sounds like he's being an arse. Secondly, having a mental illness means taking responsibility for yourself and your treatment. This can be very difficult - one of the first things you can lose is 'insight', ie the ability to recognise how ill you are - but you have to try. Unless you are experiencing psychosis, this responsibility is yours alone. Others can support, but you have to take control.
I have bipolar disorder, started getting ill in my teens. Full on, rapid cycling, psychosis at both ends of the scale, disassociation level bipolar. Not the nice, Stephen Fry kind. Despite always taking my meds, and having had loads of therapy over the years, my condition is so severe that I can sometimes get 'breakthroughs', still getting ill despite doing all the right things. I'll straight up tell you that I am a fucking nightmare to live with when depressed. My family say it's much harder to cope with than the psychosis, because it's so much more difficult to pick apart. The slide down is slower, so it happens gradually, and the symptoms themselves are difficult to read. As this has been happening for decades, everyone is much more confident about identifying symptom clusters and then standing up to me. They have to stand up to me, because I have lost insight, and either think I'm fine, or that it's just a blip, or that it's them being horrible and controlling to me (the paranoia is strong in this one
).
You're much earlier on the road here - you have no treatment/crisis plan, no access to higher-tier services, no advance directives. So all you can do is stand up to him. This is for his benefit, apart from anyone else's. Depression is terrifyingly awful. He feels scared, out of control, and dead inside. All the pointing out how much he has to be 'happy' about just sounds hollow and meaningless. It sounds like you are the one who is a bit mad, and on occasions can sound actively offensive.
Insist on another appointment with the GP. Insist on going with him. Then have a calm discussion with him. Make it clear that you are not attacking him, but his illness is dominating your lives, and is causing problems that, once he's better, he may regret for the rest of his life. Ask direct questions, focusing on the last 3-6 months, don't drag up the distant past. "In the past few months, what has your sleep pattern been like?", that kind of thing. Ask about sleep, his experience of joy (ie does he still want to do the things he used to like, and do they still make him happy), his ability to interact socially with others, his appetite and drinking, is he struggling to do basic tasks, eg use the stove to cook, how is his personal hygiene, dressing etc. Is his concentration shot? Is he absorbing verbal or written info as well as he used to? How is his driving, his ability to anticipate what others are doing, or to recognise hazards in time? The loss of sex drive is a biggie. Go through his life with a fine tooth comb. Also, ask the big one, calmly and without judgement: "Have you had any thoughts of harming yourself?" If the answer is yes, what does that look like? Does he have a plan? Is he getting intrusive thoughts? How often is this happening? Can he identify any triggers? Write things down beforehand, so you don't forget things. Make a clear list of his symptoms (I can help you put some of it into 'mental-health-speak', if you need me to). Be firm with the GP. Not to scare you, but your husband has a lot of risk factors for suicide here - his gender, age, perceived loss of status, relationship difficulties, etc. The GP should take this very seriously, and if it looks like s/he isn't, make a massive bloody fuss.
In the meantime, you need to look after yourself. From what you've written, there is a possibility that you are sliding into depression yourself. The bursting into tears at work thing isn't a great sign. Although it may seem like it, as I've been concentrating on the mh stuff here, you are not an afterthought. Please have a google, and look at some of the things that help with low level/incipient depression, and start to do positive things for yourself.
You could also google Hyperbole and a Half, Depression Part 2 (about him), and possibly Depression Part 1 (maybe about you?). They're an easy read, and a very, very good description of depression, what it feels like, and how other people can (and can't) help.
Sorry this is so long, but i hope you find it helpful! I'm a bit of an "expert by experience"
and can go on sometimes!