Hi Nic B - I feel for you in your current situation. (welcome to beyond blue btw.) It is obvious you care for your husband very much and that depression has skewed his views of the relationship(s).
Firstly, if you do a google search for...
husband refuses help for depression beyond blue
you will find other people in similar positions to you, the responses received and what they might have done as well. Unfortunately there are many stories.
as much as I could say that my father was similar your husband that was so far as talking to someone and at that time I was seeing a psychologist. I spent a day a week at their place and would tell them about the sessions I had, And one day he worked out he needed to talk to someone. I was never overt in telling him what to do.
The main thing for you though is to look after yourself as well as it can indirectly affect you - my mother found this out. Talk to your friends if it helps. Get professional help for yourself if you think it would help. It is hard to convince someone to do something they don't want to do.
One thing I can say is that you are certainly not to blame for anything going wrong. The mind plays games with us (read 'me') when we feel low - we might project our thoughts/feelings at the family in irritability, frustration, anger.
Hope some of this makes sense,