Sometimes men don't want sex because they are feeling bad- like many women. Perhaps his problem is that he doesn't think he is attractive, or he isn't able to perform as well, perhaps he's experiencing some ED problems. When men age, even if they can still perform well, they don't feel as virile and energetic, especially if he is having health problems. Maybe he needs to see a doctor? This lack of confidence might make him not want sex as much, so he avoids it. And he might not realize this, some people aren't that good at introspection
Thus, he turns to porn because it's easy- he can get sexual satisfaction that his body needs, but not experience the emotional/physical work and risk that sex requires (and intimacy).
Don't think it's about yourself unless there's a reason to, but realize that you deserve sex too. I suggest a heart to heart with him about it, focusing on what he is feeling and needs... and see if you get anywhere. Try not to bring up yourself in it, just see how he is feeling about it. Does that make sense? Perhaps by focusing him on his feelings, he will be more willing to do something about it.