I think that as soon as one partner feels the need for help both partners should go.
Divorce should be a last resort, once you've tried everything else unsuccessfully...
Some of the clear signs I had that I needed to get a divorce were that I was terrified of my spouse, dreaded his coming home, would seriously pray that he never come home again every time he left, I had no respect for him (and knew it could never be restored), I knew that living with him was harming my children and I would look at him and tell myself that I would rather die young than have to grow old with him...
Even with all that, I stuck it out for another few years to see if there was any way to work things out. There wasn't and I have been much happier since the divorce.
Rachel