My best friend and bf

So my bf made a girl account to help my friend see if her bf was cheating and he started texting my best friend and he didn’t tell me neither did she it’s on his account he made to help her and I see the messages he was the one who texted first I got mad and upset so I said hey to my friend on my account and she says I’m trying to sleep I have a reason to get mad about them texting right? Bc my bf doesn’t seem to understand that