Depends on the relationship that you have with him / her. If your "Lover" is just a friend with benies then you don't have much to say about it. If your "Lover" lives in your home and you share the bills and all then yes you can say, Hey what's up with this? If your "Lover" is your spouse then you really have a right to say something.
you let him catch you looking at **** pics sent to you by other men.
Why waste time confronting him? It's unlikely he'll change. Dump him.
Confront, of course.