I've been so tied up with a regional meeting for work the past week and have just been able to get updated with your situation (refresher - I'm the one expecting twins, with a depressed husband). I am truly sorry to hear things have taken such a turn for the worse with your wife. She does not realize how lucky she is to have someone so supportive of her and of the marriage and the kids - it is such a shame.
I know you are at your wits end, and it seems like she is continually pushing you towards the decision that you don't want to make. No one wants to end in divorce, especially when kids are involved. I am glad that you are not doing the show... I know why you considered it in the first place - hope and love.
One thing I wanted to ask - only because I have pondered doing this myself - have you ever thought about talking with her family about her depression? (Sorry, I don't know if you've ever mentioned if her family is aware that your wife is depressed) I've always gone back and forth about whether this would have a positive impact or not in my situation. I hope that it would be positive because it would further bring the problem to the surface and thus hopefully bring a support system to the situation for him. But, in reality I am guessing that it could also be very detrimental if (in his depressed state) it further pushes him away because he will feel even more lousy about himself and also because he might get upset that I outed his depression to his family. I don't know... maybe someone from this forum can comment on how this would make them feel if this happened to them.
I guess I am wondering if this step might be necessary if you are nearing a decision of seeking counsel for separation/divorce?
Please find some time in each day to smile somehow. I know it is hard, but try to find some of your own happiness, even if it's to take 5 minutes to enjoy your favorite beer or a moment to sit in the sunshine and absorb the warmth for a moment.