It's quite upsetting to see that happen, that's true but believe me, it's perfectly normal behavior. It's sort of an addiction just like smoking habit. Someone you love if doesn't quit smoking despite your effort to make him/her quit doesn't mean he/she doesn't love you. Don't think too much about it, try to take it easy and don't say NO much of the time when he advances for love making. If you pay some psychologist and ask her about your problem, you'll get the same answer "It's perfectly normal my dear. "

You should be worried, really really worried if you caught him abruptly shutting down his phone and later you found that it was some anonymous chicks on the other end. That's a big red flag but for now, he's satiating his fantasies watching porn, so take a deep breath and chillax.