John Gill Commentary Numbers 5:13

"and a man lie with her carnally, and it be hid from the eyes of her husband, and be kept close, and she be defiled, and there be no witness against her, and she be not taken in the act;" — Numbers 5:13 (ASV)

And a man lie with her carnally
That is, is suspected that he has so done, not that it is a clear case, for it follows;

and it be hid from the eyes of her husband, and be kept close ;
so that it is not known by her husband, nor by any other; "she has hid herself", so Ainsworth, being in a private place with another man, though warned to the contrary by her husband:

and she be defiled, and [there be] no witness against her ;
of her being defiled, though there may be of her being in private with such a man:

neither she be taken [with the manner] ;
or in the act of uncleanness.