Need advice

I some times go through my boyfriends phone when he's asleep. The other night I got on his snapchat and went all the way down to the bottom and I saw something weird to me. He had a conversation with someone but it didn't have a real name so idk who it was. But he had made a comment about us having problems and being in an argument. But I'm assuming it was a girl because she had said for him not to judge her because she looked ugly (I guess she sent him a snap) and he said of he didn't have a gf then he would say something. I guess meaning he would tell her she isn't ugly or something. But anyways, that's not all. He was also talking to a girl and the only messages that were saved was from her and she said she didn't feel comfortable doing (idk) because he had a gf. And he said he wouldn't tell and he would tell me he sent her a snap on accident. This was all during the summer but I don't know what to do. Because it was all literally a month before I gave birth to his baby. Should I let it go or say something? I really don't want him to know I went through his phone. I trust him but I'm not sure about all that. He promised he didn't talk to any other girls when we have fights or break ups (our break up aren't break ups, technically). It's just been bothering me a lot. Just need advice. That's all I found..