Bf has nudes in phone

I’ve been with my bf for over a year. Tonight his phone was laying in the bedroom and I opened it and went thru his pictures. I just did it for fun, not thinking I would see anything bad. I found pictures of naked women in his camera roll. Ones from before we were together and I found one from the beginning of the year (when we were together).

He has never made me feel like he would cheat on me. I am so heartbroken. I just talked to him about it calmly and he said all the pics were from before we met and he swears the one from this year was not from this year. And he deleted all of them. He said he never goes thru his pics and forgot that they were there.

Idk. I’m so heartbroken. Was it wrong for me to go thru his pics ?? Should I be mad ??