My partner has lost interest?

I've been with my partner for 12 years and in the beginning we did our share of partying and bringing extra guys in to spice things up. For the past 4 years I don't lime to party anymore and haunt brought anyone else into the bed and now my partner has not had sex with me for over a year. I've talked ton him about it and he says he just doesn't have the stimulation we used to so I got some porn and it gets him going but all he does is masturbate next to me. What do I do? We are both gay.