Asexuality becomes something to consider when a marriage has never been sexual or stopped being sexual very early on. (Of course some of the other reasons for non-sexual marriage which I raise in the related posts may apply instead.)
According to Wikipedia:
Asexuality is a sexual orientation describing individuals who do not experience sexual attraction. Asexuality as a human sexual orientation has only been recognized and defined in a few academic studies since the 1980s, and a community of self-identified asexuals has only coalesced since the start of the 21st century, aided by the widening popularity of online communities. Studies have placed the incidence rate of asexuality at 1%.
Note that asexuality is not the same as celibacy, which is the deliberate abstention from sexual activity; many asexuals do have sex, and most celibates are not asexual.
An asexual person may identify as hetero-, homo-, or bisexual, and may have romatic feelings, but only of an affectionate kind.
It can happen that one spouse is asexual has been chosen for that very reason. For example, a woman who is either sexually repressed or afraid of sex may ‘choose’ a sexually safe man – one who is homosexual or one who has no sexual drive.
Given that asexuality is very rare it can’t count as a satisfactory explanation of every asexual-looking person one encounters. And perhaps not even for all those who claim it.
There are several things to consider before deciding that someone (oneself) is asexual.
1. Is is an unconscious cover for psychological difficulties?
2. Is it the result of hormone deficiencies?
3. Is is a conscious or unconscious cover for homosexuality?