If 2 friends are fighting/arguing
http://khakisequin.blogspot.co.uk/2014/02/adviceif-2-friends-you-know-are-fighting.html (longer blog post on the topic ^^^)
You have to be patient and think of a way that both your friends can agree to disagree. Not everyone likes the same things. Maybe try and help your friends remember how well they can get along. Life is too short to be miserable and possibly destroying friendship you’ve had for ages.
Sometimes people need to except their faults in self and others before they fall out.