My heart goes out to you and I can feel the pain in your posts.
One of the central defense mechanisms people use to deal with depression is denial. People, understandably, do not like to admit that they are depressed. Others just act depressed and flat out deny that there is anything wrong. Life is too short to live it out with someone who is depressed, in denial and refuses to get help.
While denial is a maladaptive choice for a truly depressed individual, it is an unfair choice for a person with a spouse. Sadly, the problem is a fairly common one.
In most cases the non-depressed partner wants to do whatever they can to help.
Another reason that a person should not tolerate living with a depressed partner is that often what appears to be depression can actually be an undiagnosed physical problem such as a thyroid problem or other endocrinological disorder. When a person gets resistance from a depressed partner about getting help for depression, it's often helpful to start a treatment process with a general check up to rule out another medical illness. Most people who might feel it is harsh to insist someone see a psychiatrist, can make their first step by insisting on seeing the family doctor. If there is no medical problem, often the family physician will be a better candidate to recommend psychiatric treatment than the spouse of the depressed person.
I think it's fair to insist he get treatment if he wants to continue being married but this IS an illness. It is a very difficult decision for you and I hope you see a therapist for yourself. I would never tell you what to do but I would also never judge you for making the decision that you feel is best for your own mental health.