“unfaithful, yes, unfaithful.” The Hebrew text contains the figure of speech polyptoton, doubling “unfaithful” for emphasis (cp. Num. 5:6). The woman’s sin is considered very serious in the sight of God in part because of the importance of keeping the lineages in Israel known.
[For more on the figure polyptoton and the way it is translated here, see commentary on Genesis 2:16.]