please help😩 I think he's cheating...

So a little while ago, I was at my boyfriends house and he was showing me a picture and when he was scrolling through to show me another I thought I saw a naked picture of someone. I have sent him some pictures like that. But I know his wasn't me. After he found the picture he was looking for he handed me his phone. I scrolled down to the picture and kind of just kept it in the corner of the screen... as if I didn't see it. While I was scrolling he kept telling me to stop and gettin defensive. And he grabbed his phone away. When he took it back I could see him delete the picture from the reflection in his glasses. After I asked him who it was and he kept saying it was me. When I refused to believe him after a while of silence he said "I'm sorry I lied to you." And he explained about how when he got the phone (bc I just bought it for him) and he put in his email old stuff from him exes went on there and he tried to delete as much of it as he could. And that he didn't know it was there. I asked to see his phone again and I noticed he went through a few apps and deleted a lot of conversations with girls...