Dating and finding pictures

well, I'd discuss it with him...but how are you going to tell him that you saw these pics without telling him how you had snooped on him?

Here's another thought. if he received them way back then, why does he still have them on his phone or wherever?

hmmm... it's a little suspicious to me. I would understand if someone keeps pictures of their exes (non-nude of course), but there could be several reasons why he has that particular picture. They might even be a back up for black mail. Maybe she was more than "a friend" at on time. I'm not sure... You might be able to ask him under the bush and try to get around to it.

3 months is not a long time, into a relationship. The fact that it seems to have been an isolated case, my thoughts are she was "trying" to still "keep" him but he chose to stay with you.

The problem is "how" did you find those nude pictures? If you ask him politely to delete them given he is now in a relationship with you, you will from the look of it confirm that you were snooping.

That shows no trust and without trust there is going to be major issues within your relationship.

On a side note, I accidentally typed "thrust" instead of trust, lucky there is an edit button.