I don't have a magic answer for you, Brit527. No one can, with these things. But I want you to know first and formost, that any rational and remotely healthy person who has read your post is moved by your situation and amazed and your love and commitment for your SO and your strength in difficult circumstances. You've kicked arse, in the face of an awful disease in someone you love. I hope one day your partner will be able to look back and see what an amazing best friend he had in his darkest day. He got one hell of a deal, in you.

I just wanted to acknowledge that.

My suggestions, as a non-professional, but who has lived in various dynamics of mental health doo doo:

-The cannibis has to go. Mental distress often leads to coping mechanisms, some are better than others, but rarely are any worth the price of admission. Most become worse than what they were supposed to heal. It would have been nice if he had picked a hobby, and came home every weekend with a new woodworking projoct to pour himself into but he seems to have defaulted to a drug. Cannabis is not as bad some, but as Sarah Silverman says "it's a treat, not a solution". Nothing good can come from getting high on weed all day, and may even be doing terrible non-helpful things for his capacity to feel good in the long term.

Right now he needs his body in good health (ideally regular, strenous exercise, healthy diet and meditation), but also very probably medication. Which leads to us to...

• The Doctor, the TARDIS-less one. This is non-negotiable. His health has started to put your wellbeing in jeapordy and the path you are on cannot end anywhere good. I think you recognise that, and I think that should be your focus: there is not one single drug or treatment for depression disorders, and he does not seem to have remotely explored them, nevermind exhausted them. Which means there's hope, actually a bunch of it! But it's looking in the mirror time--you may even want to put it in such terms for him. He has to find it in him to save himself now. And, so help you, too (he may find it easier to try for you, at this point, than for himself). Your best bet is a mental health professional. Ideally with meds and a therapist / support group.

-Third, you need to start thinking about "saving" yourself. As strange and possibly upsetting as it feels now, there may well be a future where both of you are alive and well and living wonderful lives--as friends but not as partners. You do not owe this disease all that's good in your life, too. You cannot, in the end, save someone who does not make the choice, deep inside, to fight to live.

It doesn't have to be a 30-page plan for a new life, it doesn't have to be today or tomorrow, but your chance at living a great life (and maybe even your future kids with someone else, for example) may count on it. Start putting down some flags in your mind, where the lines are and how you would best successfully cope with moving on, etc. It's not a betrayal, at the end of the day you must be your own best friend, too.

So, how you go about it all, is up to you. Drama and ultimatums are probably not the way to go for someone used to self-defeating habits. So I would recommend framing it as a 'quest' that you're embarking on together and you are about to finally face down and battle something outside of you both and your love for one another: the depression.

Whatever you do, there's tonnes of information on reddit and around the web. Don't be afraid to learn, and to reach out. I can tell you have great strength, and a tonne of moxy. I think you're gonna be alright.

Good luck!