Hey - I am really no pro at this, but it sounds like your wife is tremendously confused based on her behavior as you have described it. One thing is for sure - you are not going to get her to change her mind about leaving, and the more you challenge her about it the more resentful she will become of you questioning her choices. If she must leave, let her leave without question and then work with things from there. It stinks, but there is nothing you can do to control it.
Also, you probably need to strap yourself in and realize that this is a process that could last awhile - it certainly is in my case and it has been filled with ups and downs. Some I have met well, others not so much. I am giving you adivce that I have a hard time taking myself, but patience....used as much as you have, and when you run out - use more. Ultiamtely, you decide when to throw in the towel.
Have you taken a deep look at some of her complaints? Owned them? Accepted them? Worked to 180 them if you can?
Regarding the depression/bi-polar thing, try to stay off that road. I went there, and it leads nowhere at all. If true, there is nothing you can do about it and I would strongly suggest you don't bring it up to your wife. Work on the only part of this equation you can - you.
All hope is not lost, but chances are this won't be a quick fix.
