Although you haven’t said it, I would venture a guess that your other breakup was something that happened to you rather than you deciding the relationship should end. I am making that assumption, because the depression you described sounds like it was exacerbated by the fact something happened that you did not have control over. If this is familiar I would take a different tack and control what you can, which in this case may be calling it quits on a mediocre relationship. As lovely and wonderful as your lover is–she has been systematically unfulfilling.
Why would you move in with a woman you don’t trust, has told you she isn’t fully committed to you, and who has tried to break up with you twice in recent times? I would rather see you get involved with group therapy in your area that will allow you to cushion the blow of the losses of the relationship. But in any case I wouldn’t wait for things to deteriorate to the point where she ends it.
Of course there is the possibility that she doesn’t want to be the one to pull the plug, but then you are left in the position of engaging in something that is disintegrating rather than flourishing. It seems unwise to move in when the relationship is at its lowest point.
Rather than wait for the inevitable distancing that will happen when your affection and caring become unbearable to her, I would do something about it now. Living together requires more than a take it or leave it attitude. I would definitely reconsider moving in and take the hit upfront. From everything you say a greater devastation is coming your way if you live together now.
If she is willing I would strongly suggest couples counseling before you attempt to move in. I think discussing these matters with the help of a professional before the feces hits the oscillator would be a good idea.
Wishing you patience and peace,