There's nothing wrong with it as such, but I find it telling that he said "Come in" before the screen was turned off, and that you managed to see the image.
He wasn't really "caught" watching porn, since he gave you permission to enter the room while it was still on the TV.
Maybe the fact that he was pretty candid about what he was watching means that he doesn't thing it was a wrong thing to be doing, or something to be ashamed about and hide from you.
It's not like watching porn is the same as cheating on your partner, tell you Mum if you it help make you feel better, she'll probably appreciate your loyalty, but it's not really a big thing and you can't be 100% sure what he was watching (a topless woman doesn't instantly mean porn, it could have been any number of films).
Maybe you should talk to him before getting too flustered about it.
He wasn't really "caught" watching porn, since he gave you permission to enter the room while it was still on the TV.
Maybe the fact that he was pretty candid about what he was watching means that he doesn't thing it was a wrong thing to be doing, or something to be ashamed about and hide from you.
It's not like watching porn is the same as cheating on your partner, tell you Mum if you it help make you feel better, she'll probably appreciate your loyalty, but it's not really a big thing and you can't be 100% sure what he was watching (a topless woman doesn't instantly mean porn, it could have been any number of films).
Maybe you should talk to him before getting too flustered about it.