They probably know. All you need to do is keep it remotely hidden so that you avoid any awkwardness, after all they probably don't care but this doesn't mean they want to discuss it with you.
I say, like others here, that you should share it. Approach him before he tells your parents and ask him just what he thinks he has on you that could drop you in it.
Set him up with a password or whatever for the porn and games folder. If he still thinks porn is bad and if he is in any way homophobic a quick "Jeez, what are you, gay?' might persuade him that porn is great.
Good luck man...
