Leave him?

I got bored and I went on boyfriends Snapchat while he was sleeping bc why not and then I opened a convo he had with a couple of friends and basically 2 of his friends sent some girl's nudes on there and he screenshotted all the pics and I've honestly never been so confused on what to do. Is this cheating in a way? I'm still in shock and haven't been able to sleep , please help