I am SO SORRY that you are in this situation. I had hoped I was the only one, I would not wish this on my worst enemy. Here is what I did to get dh help:
1. Count his pills. All of them. Make sure he is not taking more ambien than needed. I found my dh was taking more Ambien than needed which caused the sleeping issues. If dh is misusing meds his doctor can have him committed.
2. Go to every dr appointment with husband. Let your dh know that you are going in to see the doctor with him. Let the doctor know exactly what is going on in the house and that the meds are not working.
3. Call his therapist before each and every one of his appointments and leave a voice mail message about what has happened between visits.
4. Call every friend your husband has and tell them exactly what is going on in your husbands life. I called two of his friends who hauled him out of bed and to the local psychiatric hospital. They assessed and admitted dh for four days.
All in all I have to say it has been a lot of work for nothing.(I am in a particularly bitter mood this morning due to his response to our 17year olds neuro problem she developed in the last 48 hours). He is going to the local day psychiatric program about 50% of the time. The rest of the time he is in bed.
What has helped me is knowing I have done all I can. Going to the library and getting books about supporting your spouse through depression. This website and the anne sheffield website about depression fallout. Plus my best friend who calls me every day to check on me and lets me tell her exactly what is going on. I try to stay on a monthly schedule with me psychiatrist, it is too expensive to go more often than that.
I hope your situation turns out better than mine is.