Surreptitioussexual is a sexuality where one doesn't share their sexuality because it feels very emotional, personal, and/or spiritual to oneself. Not that the sexuality is irrelevant to oneself, but they just don't feel comfortable sharing it.
The romantic counterpart is surreptitiousromantic.
History
This term was coined by Fandom user Vic978 (now KadeButton22) on February 22, 2021