You guys I really dont think I can hold out any longer. I feel that I have to confront her about the affair.
Ask yourself what your overall goal is (to save the M?) Then ask yourself "is what I am about to say/ do moving closer to that goal or farther away?" Not just for the above, but for EVERYTHING.
Now, please describe what you hope to accomplish by confronting her, and why you think confronting her will give you that result.