Half naked pics of girls on his phone?

So the other day I asked to see my bfs phone for something (I think it was for an app we both have but mine was being weird, so I wanted to check something ) and he got all weird about it, so I just dropped it. But today while he was having a nap, I noticed his phone in the living room...and I couldn't help myself. I snooped. I went to his pictures and there was half naked chicks with the snapchat thing to add them, I didn't go into his snapchat or anything cause I sort of just didn't know if I would like what I found.

-So should I just leave it? Like guys will be guys, it's no big deal.

-Tell him what I saw, tell him how it makes me feel and probably get into an argument about me looking in his phone

I'm just really conflicted about the whole thing