Perhaps you could recommend an even better subreddit for him: /r/nofap. I don't have much experience with relationships (I'm still relatively young) but I was watching porn regularly for nearly a decade and up until I met my (now ex) gf. After an embarrassing incident over videochat (i.e. Skype sex) in which I simply wasn't able to get it up after having watch lots of porn and jerking off, I knew I had a problem. I faked an orgasm because I didn't want her to think I was inadequate or she wasn't adequate for me... It was one of the most traumatizing experiences of my life and I quit watching porn cold turkey right then and there. I haven't watched porn in over 6 months nor do I plan on ever doing so again, and although I don't really mind if other people do, I believe that at least for me, it reduces intimacy in a relationship. Perhaps if both me and a future partner are present and watching consensually then it'd be fine, but I don't think I'll ever get to that point. I later broke down crying and came clean a few months later, and fortunately she forgave me. Unfortunately, we broke up for unrelated reasons, but I'll never forget the shittiness of what I had done.

On to my point: It seems like a given that you're going to confront him about this, sooner rather than later. When you do, you could breakup with him right then and there, which I imagine would be extremely difficult and heartbreak. Or (and let me preface this by saying that ultimatums usually have no place in a relationship) you could tell him what you discovered, how it made you feel, and that if he continues this type of behavior (commenting on /r/gonewild pics or watching porn in general) then you wouldn't want to continue being in a relationship with him. This should be a major wakeup call for him, and it gives him the option to modify his behavior. If he loves you, he most definitely will. It may be difficult rebuilding trust, and salvaging the relationship, but from what you've described, it seems like a possibility. I wish you all the best.