Or maybe the signs of his sexual sluggishness were there all along and you just assumed things would get better - but if anything, they've gotten worse.
According to psychologist Asiphe Ndlela, different people have different levels of interest in sex and once the initial spark of a new relationship settles into routine, the sex settles down too.
She says it's estimated that one out of every three couples has this difficulty. She says one study found that 20 percent of married couples have sex fewer than 10 times a year.
Ndlela said a low sex drive is the number one problem clients bring to psychologists and sex therapists.
"Sex is an extremely important part of marriage. When it's good, it offers couples opportunities to give and receive physical pleasure, to connect emotionally and spiritually. It builds closeness, intimacy and a sense of partnership.
"It defines their relationship as different from all others. In short, sex is a powerful tie that binds," Ndlela says.
"This lack of sex is more than just a lack of physical attention. It goes deep into a woman's heart."
Ndlela says unless the couple gets help they often end up divorcing.
"Many individuals want more than they get at home and end up looking elsewhere for it.
"The individual in need of more intimacy feels like a child sneaking around to get something that is very important to them as a human being.
"Usually the woman with the higher sex drive just lives her life in lonely misery. Eventually, feelings of rejection become increasingly difficult to manage. Sadness turns to anger. Those yearning for more physical closeness vacillate between being distant and unpleasant."
Ndlela says though these behaviours are merely symptoms of underlying hurt, people with a low sex drive don't perceive their partners' behaviour quite so compassionately.
"Empathy is usually in short supply. Arguments about sex, or the lack of it, become the norm. Blame-slinging disagreements add to the already icy distance.
"Then, it's not long before their bitterness and animosity collide head-on with every other aspect of their relationship. Nothing seems right anymore.
"Most men who have low sex drive problems are unwilling to talk to their wives, or ask for help.
She says this is because to be disinterested in sex is to feel less than a man.
"Just thinking about low libido, let alone talking about it, strikes terror in men because it threatens the very foundation on which their feelings of self-worth are based. No wonder they do not talk about it."
According to Dr Zinzi Mbuqe, a GP based in East London, most women blame themselves.
"Most women feel they are no longer attractive but mostly the partner's indifference to sex probably has nothing to do with how attractive they are or how much their partners love them."
She says the man might have a personal issue, and might suffer from depression or stress. Or the problem could be an illness, obesity or trouble maintaining an erection.
Many men lose interest in sex for the same reason many women do: unresolved anger, resentment and hurt.
Medication could also be a reason for a low sex drive.
"For example, most anti-depressants dampen desire and the ability to be aroused.
"Cardiovascular disease of any sort is a problem too, as well as some of the medication that treats it," Mbuqe says.
She says hormonal fluctuations such as testosterone, also affect sex drive. She advised that a man experiencing a drop in desire should visit his physician for a thorough check-up.
Mbuqe also referred to emotional problems as a reason for low sex drive. Depression or family history of sexual abuse could be causes.