Having been cheated on more than once, I know it is a symptom of a greater issue, one that a wife or husband may not even know exists. So no, another can not break up a marriage per se, but let me ask you this...if someone wants to be with you so badly that they're willing to leave their marriage, wouldn't you want to make them totally leave that marriage to prove how much they want to be with you? I figure if I'm worth loving, you should be free to totally love me, no strings. And another thing I've learned, especially about women, we want what every other woman has, and it's a boost to our ego to get it, even if we don't really want it once we have it! (Yes, women have an ego too!)