You poor thing. I feel for you, and let me share some experience with you.
I think you first have to understand that guys are basically hormonally charged. It's no excuse for licenstious or promiscuous behaviour however once in a while, a guy tends to uncontrollaby shift his gaze to the girl next to you, or have dirty thoughts running through his mind, or even turn to porn to satisfy these desires. These are biological, innate desires, no matter the label. So you can't really fault him for it.
That said, I think its wrong to discuss with the gf about the porn he watches. It's downright disrespectful and hurtful. No one should ever have to go through the extremely hurtful and traumatising experience of listening to his/her love one describing someone esle's naked body or sexual act. It's abhorrent absolutely. In this regard, I suggest you talk to him. Tell him that you feel uncomfortable about him saying this to you, and tell him you feel hurt when he's actually looking at other female. Its kind of like cheating on the you.
I think its possible to watch porn and at the same time have a completely lovely, healthy relationship with one another. Many guys still tune in to porn regularly even when in loving relationships simple as an avenue to relieve their sexual urges.
The bigger problem here, I suspect, lies in the fact that he seems to be into you for the lust rather than the love. You have to start to question whether his is true love or plainly just for the sexual experience? It seems to be the pre-relationship him and the post-relationship him are radically different. This means he is truly not the person you have fallen in love with. The person you have fallen in love with is just a veneer.
I know its difficult, but what determines whether a guy truly loves his girl is not during the wooing phase, or the honeymoon period, but during the post honeymoon period when a guy's respect, patience, maturity, responsibility comes to test. Love in its post-honeymoon stage isnt all lovey-dovey, it takes responsibility, maturity, commitmment and mutual respect to sustain it.
Talk to him, and if things don't change, dont drag it any further. You deserve a guy who will love you unconditionally and eternally, not some opportunistic guy who only love you to get you into his arms [or into his bed], and then change 360 degrees thereafter.