Wiktionary
n. 1 The state of being monosexual. 2 (context countable English) A sexuality that involves attraction to only one sex: generally, homosexuality or heterosexuality.
Wikipedia
Monosexuality is romantic or sexual attraction to members of one sex or gender only. A monosexual person may identify as heterosexual or homosexual. In discussions of sexual orientation, the term is chiefly used in contrast to bisexuality, or various other non-monosexual identities. It is sometimes considered derogatory by the people to whom it is applied.
The Kinsey Reports found that, in experiences leading to orgasm, 63% of men and 87% of women could be described as "exclusively homosexual" or "exclusively heterosexual".
Usage examples of "monosexuality".
Perhaps Priestess Poogli is a throwback and senses somehow that this latter-day monosexuality is like a last gasp of a dying civilization and that, food or no food, unless there is a return to the duosexual era, the race of Sacred Fishers is doomed.