OK I admit I have confronted, pursued, and thrown hissy fits when I try to set a boundary.
Does a cop throw a hissy fit when he issues you a citation, or does he just issue it?
Real men don't yell, scream, or "throw hissy fits" in order to set a boundary, Ken. Very calmly say "I will not live in an open marriage. It's incredibly disrespectful, and I value myself too much to tolerate it any longer. If you don't end it, immediately, then I will immediately begin to take measures to protect myself."
And make sure you're not PAYING for ANYTHING that she's using to carry on her affair -- cellphone, computer, internet, etc.