What would make a boyfriend treat your friends bad?

My ex used to treat my friends badly, not always overtly. One time we he drove my friends to a restuarnt and he got lost and so angry that he slammed his cell phone on the passenger side floor where I was sitting, it grazed me. he's done this before too. Whenever a friend comes over or we go out he gets very angry. He's been so abrasive to my friends that some of them have told me to leave him, which I did eventually. He has something bad to say about all of my friends. One day I was so angry I shouted you f'ing alienated all of my friends and they no longer call me. He seemed to be upset but I'm not sure if it was the fact that he did alienate my friends or because I was mad at him.