Why don't you just sting her along. Talk to her but not see her. Find a friend and introduce him to her and see if she does the same thing to him.
Sort of like the new trick in North America.
Use a private detective to see if the spouse succumb to temptation.
Once she is exposed, no more problem

7Siu: I am not even sure I know which trick you are talking about.
You have so many, many tricks that I will need to write them down on my Palm soon.

I am referring to the new "catch your spouse" industry in the U.S.
Find a detecctive, go to the favorite bar of the husband/wife. Get the detective to try to seduce the spouse. It is a test of "f*ckability" rather than actually doing it.