I think if you have a good solid, honest relationship; the chances of this happening in zero to nothing. But, if you are insecure, dishonest or manipulative it would be hard to feel secure with your man, especially if you stole him away from another woman. You see these scenarios all the time on shows like, "Jerry Springer" reality shows, and tabloids. How could your sister or best friend sleep with your husband? Why would the person you trust and feel closest to betray you in such a way?
This is ultimate betrayal and one that is hard to forgive and get past, but I feel if your man would be stupid enough to betray you in such a way, then let the bitch have him! On the other hand, maybe it's you that you need to take a good hard look at and make sure you are indeed taking care of your man, communicating your needs honestly and living with integrity.
I knew this woman who went after a married man when he was vulnerable and confused. She seduced him away from his wife and ultimately married him, but she never felt secure. She was always jealous of any female friends he had and need constant attention. She ended up cheating on him with several men before leaving him before he left her. So in the end of the day, was it worth it? Having this karma attached to you in my opinion isn't worth it, so don't do it! Don't think about it and if some bitch does try to pull this on you, just put on that Loretta Lynn song and sing it out loud!