[Melusine]

Sorry to hear your story Faceman - it sucks when one of your friends suddenly shows a nastier side to them that you'd never have expected them to have.
I agree with pretty much everybody here: those societal (non-)arguments of his are just plain BS. If he would continue to live along those rules of his, he should prepare to lose a lot of his friends, so you might as well give him a hint by telling him that if he isn't going to come clean with the cops, you or Y will do it for him. Maybe that will be enough of a wake up call for him to realise his error. And if not, well, I think he deserves the consequences. It's not that I think the original problem is so bad, where I live pot isn't even illegal, but the point is that he caused your friend Y to be in a bad situation. Especially if there's a chance this will have consequences for his work and stay permit, that's bloody serious!
In this case, if after a lot of convincing X still would stand by his so-called rules, I think I would have no qualms of turning him in just to protect your other friend. What's more important, a stupid fine or Y potentially being out of a job or place to live??