My Boyfriend Not Interested Anymore!

my boyfriend of 2 years (he is 56 and i'm 47) rarely wants to make love. i feel like i'm not desirable anymore. he says i'm not the problem, that he just dosn't have the desire to perform. what can i do to boost his love making desire and performance? i think i've tried everything. Is It impotence, libido, low testosterone or physicological? help, please.