Put on a Shelf
My husband has completely lost interest in sex with me. He claims he's too tired all the time. He works a lot in a hot environment (and I don't mean "hot" as in "sexy"). Despite these long hours, he masturbates three to five times a week, usually with porn (movies, magazines, etc.) He always hides it from me. How do I face this when it hurts my feelings so much?
It's dangerous to generalize about the differences between the sexes because you can always find a man who shares the qualities you attribute to women, or vice versa. But I'm going to do it anyway because I think it might help to save your marriage.
Men find it easier to compartmentalize their sexuality than women do. This is why some men can carry on an affair or hire a prostitute and convince themselves it won't have any effect on their marriage. Your husband thinks of masturbation as something entirely separate from his sex life with you. And in a way, he is right. During masturbation, he only has to think about himself, not about your pleasure as well. He can watch porn and enjoy the novelty of fantasizing about bodies he has not seen before or acts that you might not enjoy performing. Masturbation can be a quick and easy way to relieve some tension. Bringing his wife into sex is too stressful for him right now.
Of course, a part of him knows that he can't really compartmentalize masturbation, which is why he is hiding (or trying to hide) his jack-off sessions from you. His libido is clearly still reasonably high, and he's able to get an erection and ejaculate. So there's no physical reason why he couldn't have sex. Basically, he's sending you a message that he doesn't want to have sex with you any more. I'm not sure why, but work alone isn't a good answer.
Couples often stop having sex because they have disappointed one another. Resentments have accumulated until the thought of being physically close or vulnerable is unpleasant. Couples counseling would be the best way for your husband to ventilate some of his anger. I'm sure you are quite angry as well. He may be unsure how to approach you, knowing that you feel hurt and rejected. He's being a bit cowardly and avoding your understandable frustration.
Masturbation and lovemaking with a partner fulfill slightly different sexual needs. So I believe that most people continue to masturbate even if they have a good sex life with their spouse or lover. But if lovemaking has stopped, and the solo sex continues, communication in the relationship has broken down.