If I am blunt I'd be able to get on with my next relationship unencumbered by a marriage.
Do you believe if you were divorced right this second that you would be "unencumbered" by your relationship with your Wife? Paraphrasing Cadet, it's not fair to anyone to start a new relationship until you're done with this one. The physical and legal act of DIVORCE doesn't really signal the end of this relationship...unless you want it to be. Yeah, legally, I guess it does, but that's not so important, huh -- you're W is in a new relationship now and you aren't even filed to be divorced, right?
If you have some physical, emotional, or financial reason to file for divorce, go ahead and file. But if your goal is to save your marriage, I don't see the benefit.
And PigPen - I'm not the master of anything. Everything I know has come from others who walked this path before me.