If he is "hiding" his viewing of porn, then it is cheating, since normally porn gives the one person ( normally men) the wrong idea of what a healthy sexual relastionship can be, and normally lowers the value of women in their eyes, Plus if often hurts their performance in the bedroom.
So if he told you, he wanted to watch porn, and you said ok, you did not have a problem, it is not cheating, if he is hiding it, he is ashamed and it is cheating.
Some couples enjoy watching it together and acting some of it out, while not my Christian idea of healthy sex, it is sometimes recommended for couples having some issues in those areas
I don't know what exactly was his "teen porn" but in general it sounds like he did not have a healthy idea of sex and he is better off without you.