First, let's clear something up: he's the only one who has admitted to you that he watches porn. The rest did too, they just didn't tell you.
To answer your question, watching porn doesn't make somebody more or less likely to cheat. That's an entirely different set of circumstances: there are faithful husbands and boyfriends across the nation with porn on their hard drives. However, you are right to be irritated because he's being a massive jerk about it.
You need to talk to him about what a pig he's being, basically. Tell him if he wants to watch porn, to just not discuss the subject with you or watch those butt-shaking videos in front of you. Tell him how you feel and ask him to be more discreet about it, for the sake of your feelings.
It sounds like she wants to watch it with him and he turned her down point blank. Obviously porn can't always be a couples activity, sometimes a person just needs some alone time and porn, but maybe she'd feel more comfortable if she felt more included in this side of his sexuality. Maybe not the butt shaking videos, but if they watched porn together and it led to them getting it on, that shouldn't take all the fun out if it for him.
If that's the case, OP, let me know, but either way, he needs to handle the situation with more maturity. If she wants to watch porn with him, he can move over on the couch, for Pete's sake.
He don't watch it on tv. He watches it on his phone. He says he's aloud to do whatever he wants on his phone. I just want him to let me watch it with him sometimes. I got him a porno for Xmas and he don't even like it. He only watched it once. He says he don't like it cuz it not interesting and he only like pornos with black people. When I asked him what type of porno he wants he said it didn't matter. He's so confusing.
He's not confusing, he's being a complete and utter jerk.