Okay ITS ABOUT A BOY???.....WHAT ELSE?

Okay so I went shopping yesterday with my bf and we went into AE and i was looking around and i found this dress and my bf wanted me to try it on so I walked into the dressing room tried it on I walk out and there stood my ex......he looked at me and said I would take you over my gf any day and then i saw my bf coming at me and looked at my ex and then just left the store! I hurried really fast out of there to find him and as I was running I saw this huge crowd and i didn't care till i heard my bf yell Jack*** stay away from her! then i saw that my bf and my ex had gotten into a fight and everyone was watching and it was horrible.....I went down to get my bf and we drive home in silence untill he asked me what I was doing showing my ex what i looked like in the dress. I told that I came out to show him but there he stood. and then we he dropped me off and sped away! my question is what did I do? what can i do? and why is he so piss ed?? I need help...anything