If you are to the point that you don't think the marriage can survive, then you have nothing to lose by laying out to her what you want in life and relationships - while respecting what she wants in life and relationships. You may just come to the conclusion that even though you love one another you are fundamentally different regarding lifestyle.
You stated she is driven to "hang on," so I would make it clear that the issue at hand isn't a problem with the basic relationship between the two of you, but in that you find it easy and desireable to love more than one. Make it clear that this will not change - and that there is no point in hanging hoping that you will change.
Given her jealousy, she currently does not have the skills for poly, but they could be developed if she is interested in trying. That said, if she is truly mono, it will be very difficult for her to come to terms with you being poly (although we do have some poly-mono configurations on the forum), and she may be happier not dealing with it at all.