a lot of marriages the sex is dead. someone can bring up the stats of sexless marriages and its a big number. but even if the wife is doing her job at home in her eyes it doesn't mean she is.. guys still want to excitement of being with someone new and the fantasy of doing things that the wife doesn't do. example many American wives don't give head, but she will ride you like a stallion.. so the man will stray outside the marriage to fill that void he is missing. its as simple as that and not complicated.
I wish the OP well, just remember that just cause you think you were satisfying your hubby doesn't mean he was satisfied.. and even if you were there is a rush of meeting someone new and screwing her brains out then leaving.. its something males have evolved to do. hitting the same pussy gets boring after a while.. and yes the porn addiction your hubby had can contribute.. with porn you can bring up any genre you want or fantasy.. and then with hobbying you can take those fantasies into real life and not worry about the wife saying "I can't tonight honey, I have a headache"