Friend wants me to back him up?

Jeeze I have a friend who's with this girl and her ex husband is damn crazy and wants to fight my friend. So my friend text me asking to bring him to kick his *** and back him up incase. I have my cousins wedding next week and I'm best man, and I am a single dad and a car that needs fixing I have so much to do and hate this drama!!! He had the mind to say I am a bad friend and blah blah blah what should I do!!!