I sympathize with your situation. It would seem that the real thing with a partner would be better than masturbation with porn. At least he recognizes that it is a problem. This is largely his challenge, since he will have to change his behavior and stop his excessive masturbation with porn. Perhaps you both could conduct sexual activities in the morning, before he has a chance to masturbate during the day or evening, before he uses up most of his sexual energy. Once he is sexually active early in the day, maybe masturbating later will not have as much attraction for him.