When I last spoke with my friend I told him I found his girlfriend's nudes.
Why would you do that?
He was being such a dick to me, I also once told him about his gf's sexual dreams about another guy
That is not a good thing to look at. You should respect your friend and not take looks at his girlfriend.
Nah, I'm going to tell him about it.
You can tell him about it, but you shouldn't look at his girlfriends nudes as that's very distasteful. I doubt she intended for you to see them, so you should just move on after telling him about it.