Is he cheating? What to do?

This came on my bf snapchat and also was sent to me. when I asked him about it he said shes just his friends friend just wanted to see his phone n did it n said he snapped at her . He deleted it straight away I looked her up n found out she's actually not in his friends list on fb so I calmed down and told him since your not friends I don't need to worry. But I found out today he has her as a friend on snapchat which he never mentioned? Her name is amy. But also Were hiding our relationship from his dad cuz he doesn't like me so I found out my name on his phone is Amy n he said he just couldn't come up with a name?? Should I be worried? What ye think :/