Killing anyone who is a clear threat to your territory.

Hence why one should attempt to induce the girl to break up with her boyfriend, rather than attempt to induce her to cheat on him. As you point out, that has a distressingly high chance of ending in murder.

If you are going to go around seducing women who have boyfriends don't try to sugar coating it by pretending it always means that the relationship was unsatisfying.

I don't swing that way. Regardless, I suspect our disagreements about the axiom are definitional. The terrible thing about satisfaction is that it is relative; it seems fair to say that one who willingly ends a relationship does it because it is unsatisfying. If it was made unsatisfying because one put forward a better offer, I have a hard time seeing that as villainous. (If one is fraudulent about the quality of the offer, that fraud is villainous- but that's a separate issue from the BFD.)