All 3 Uses

chaste
in
Exit West
(Edited)

Saeed had once more asked her to move in with him and his family, telling her that he could explain things to his parents, and she could have his room, and he would sleep in the sitting room, and they would not have to marry, they would only, out of respect for his parents, have to remain chaste in the house, and it would be safer for her, for this was no time for anyone to be alone.
p. 74.2 *

chaste = sexually inactive
...the idea of living as a chaste half lover, half sister to Saeed in close proximity to his parents…
p. 74.8
The following night, or perhaps the night after that, Saeed entered Nadia's room and they were unchaste there for the first time.
p. 85.7

unchaste = sexually active

standard prefix: The prefix "un-" in unchaste means not and reverses the meaning of chaste. This is the same pattern you see in words like unhappy, unknown, and unlucky.

Definitions:

(1) (chaste as in: remained chaste)
not having sex; or not involving sexual desire
The exact meaning of not having sex depends upon context. It can mean
- to be a virgin (never have sex)
- to be sexually inactive currently or for a long time
- to not have sex outside of marriage
(2) (meaning too rare to warrant focus)
Much less commonly, chaste can refer to an unornamented simple style.