First and foremost the man feel's he is a failure & he tries to put the blame on his partner saying she has not co-operated in a right manner or she is not showing interest like earlier etc.. This is just to satisfy his ego. At this moment woman has to control her emotions and make him feel comfortable saying "not to worry & we can try it later when you are more relaxed". Yes, it's not fair to always expect woman to be more understanding but after all the love & pleasure is equally shared.
At the same time Men should accept the fact that their libido & vigor are deteriorating which is basically due to hormonal chages along with the age which is quiet common. One more reason of ED could be Diabetis. While administering the aphrodisiacal medicines will help attaining the required erection, keeping the mind calm without anxiety is the pre-requisite.
Mind you, to have a great sex the important organ is mind not the other parts of the body. Man should not feel shy or disappointed if they fail to achieve an erection or ejacualates prematurely. They can use fingers or even may opt to satisfy his partner orally.