My boyfriend has nude pics of his female friends in his email... Is this cheating or what? Is this okay?

We've been together for 8 months and we love each other very much. We even already talked about having a future together. He was my old friend. Then we started to going out last year. But he lives in las Vegas and I live in Illinois cuz he moved. We text messaging each other everyday, we always talk. We send letters and gifts on occasions. But, when I opened his email, I found out that he got nude pics and v*gina pics of his female friends. I feel betrayed and hurt. But he does have pics of me being naked and being dirty in his phone and email. Still, why does he have those pic of his female friends? Is this okay? Explain it please. It hurts me. He's 17 and I'm 16. Does this mean he's cheating? Help me somebody. :/