Let's take the worst case scenario: Your girl is a slut who brings home a disrespectful POS she has been fucking.
What do you do? You kick them out of your house. Violence is especially unneeded and a bad idea when you are a TRAINED fighter and the dude is a restaurant worker. Even in this scenario where a guy who is fucking your girl shows up with her and treats u like an a-hole, you are still wrong and STUPID for attacking a guy you can EASILY beat the dog crap out of.
And my guess? This worst case scenario wasn't the real situation by a long-shot.....