It's a total myth that men are horny 100% of the time. It's only 99%. LOL. Jean has sent a link to a very interesting article from the UK Daily Mail about women's low libido. (Why is it that our papers here in the US don't write about these things on a regular basis?) And, ironically, those same symptoms are what causes guys to lose interest, too.
Lose interest in sex? Men? Yes, we do. It's okay to admit it. We should admit it. It's to our benefit to admit it. Let go of that machismo attitude and say it. We go through life changes and challenges that can totally affect our interest in sex. Dr. Rachel Carlton Abrams describes low libido as a "lack of spontaneous desire for sex" that includes masturbation.
Her eight reasons are: Repressed sexuality (upbringing); low body confidence (low self-esteem in appearance); previous trauma or bad sexual experience (molestation, or a really bad early experience); painful sex (overly sensitive glans, or testicular pain during ejaculation); low testosterone; underlying medical issues (remember boners are our barometer); stress and being "too busy" (self-explanatory); lack of trust (we have lost trust in our partner(s).
Each and every one of those can (and do) cause a low sex drive in anyone - man or woman. There are no resolutions offered in her article. But suffice it to say that a lack of interest is a health issue - whether mental or physical - and you should see your doctor.
Speak openly, frankly, and work together to solve the problem.
Then get back on that horse, whatever your preference for release.