don't know what to think..

So me and my husband bicker like any other couple out there. We've had our differences here and there and set rules for each other on social media (no cheating involved). We agreed to only add our good friends we talk to or at least tell the other if we do add someone of the opposite gender. I went through his Snapchat and asked why there was girls he doesn't talk to added. He got defensive and immediately told me to stop. To delete my guy friends he knew about. I don't understand why he would get so upset. Any advice? Am I wrong to even go through his phone?