For both your sakes you have to step away (properly).
Tell him you'll support him as a friend (but not on 24 hour call) but that's it. No more paying for things, no more solving all his problems, no more being his parent and carer.
He needs proper help otherwise he will never take the steps HE needs to take to start improving his life. If he loves you he'll be prepared to get (and stay) well for you, but more importantly he has to want it for himself.
I can hear how much this is wearing you down - physically, emotionally, financially etc and in being kind and supportive, and trying your damdest to be a good girlfriend/partner, you're doing you both a disservice by allowing him to be completely dependent on you and that, in turn, is making YOU ill.
Self-preservation mode switched ON.
Put yourself first. Mo ifs, no buts.
You can't help him if he won't help himself, and he won't help himself whilst you're helping him to this degree.
You've been nothing but kind, loving, loyal and supportive. You've tried your very, very best, but it'll never be enough whilst he needs lots of professional help.
I have sympathy for him - depression and other mental health problems are utter HELL to live with but he has allowed himself to totally depend on you and now it's time for him to acknowledge that he needs to do things to help himself now.
This life for both of you is completely unsustainable.